Polishing pad and method for manufacturing the polishing pad

ABSTRACT

Disclosed herein is a method for manufacturing a polishing pad, including the step of filling the interior of bundles of ultrafine fibers which have an average fineness of from 0.01 to 0.8 dtex with a polymeric elastomer having a glass transition temperature of −10° C. or below, storage moduli at 23° C. and 50° C. of from 90 to 900 MPa, and a water absorption ratio, when saturated with water at 50° C. of from 0.2 to 5 mass %. Also disclosed herein are polishing pads obtained by the method above.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Non-provisional applicationSer. No. 13/058,016, which was filed on Feb. 8, 2011. U.S.Non-provisional application Ser. No. 13/058,016 is a National Stage ofPCT/JP09/063802, which was filed on Aug. 4, 2009. This application isbased upon and claims the benefit of priority to Japanese ApplicationNo. 2008-205981, which was filed on Aug. 8, 2008.

TECHNICAL FIELD

The present invention relates to a polishing pad, and more particularlyto a polishing pad for polishing various devices, substrates and otherproducts on which planarization or mirror polishing are carried out,examples of which include semiconductor substrates, semiconductordevices, compound semiconductor devices, compound semiconductorsubstrates, compound semiconductor products, LED substrates, LEDproducts, bare silicon wafers, silicon wafers, hard disk substrates,glass substrates, glass products, metal substrates, metal products,plastic substrates, plastic products, ceramic substrates and ceramicproducts, and to a method for manufacturing the polishing pad.

BACKGROUND ART

In recent years, with the increasing levels of integration andmultilayer interconnection in integrated circuits, there has existed aneed for high-precision flatness on the semiconductor wafers where theintegrated circuits are formed.

One known process for polishing semiconductor wafers is chemicalmechanical polishing (CMP). CMP is a process for polishing a substratesurface to be polished with a polishing pad while slowly dispensing aslurry of abrasive grains onto the surface.

Patent Documents 1 to 4 below disclose polishing pads adapted for use inCMP which are composed of a polymer foam having a closed cell structureand being produced by foam molding a two-component curing polyurethane.Because such polishing pads have a high stiffness compared with thenonwoven fabric-type polishing pads described below, they areadvantageously used in, for example, the polishing of semiconductorwafers requiring high-precision flatness.

Polishing pads composed of a polymer foam having a closed cell structureare produced by, for example, subjecting a two-component curingpolyurethane to a cast-foam-molding. Because such polishing pads have arelatively high stiffness, convex parts on the substrate being polishedtend to incur selective loading during polishing, resulting in arelative high polishing rate. However, when clumped abrasive grains arepresent on the polishing surface, because such clumped abrasive grainsalso selectively incur loading, scratches are readily formed on thesurface being polished. In particular, as described in Non-PatentDocument 1, when a substrate having copper wiring that is scratchedeasily or a material with a low dielectric constant and with weakinterfacial adhesion is polished, there is a particular tendency forscratches and interfacial separation to occur. Moreover, in acast-foam-molding, because it is difficult to uniformly foam a polymericelastomer, variability tends to arise in the flatness of the substratebeing polished and in the polishing rate during the polishing operation.Moreover, in a polishing pad having closed cells, the voids thatoriginate from the closed cells become clogged with abrasive particlesand abrasion debris. As a result, when the polishing pad is used for anextended period of time, the polishing rate decreases as abrasionproceeds (this characteristic is also referred to as polishingstability).

Patent Documents 5 to 14 disclose, as a different type of polishing pad,nonwoven fabric-type polishing pads obtained by impregnating a nonwovenfabric with a polyurethane resin and wet-coagulating the resin. Nonwovenfabric-type polishing pads have an excellent flexibility. For thisreason, when clumped abrasive grains are present on the polishingsurface of a substrate being polished, the polishing pad deforms,thereby suppressing the selective loading at the clumped abrasivegrains. However, the polishing characteristics of nonwoven fabric-typepolishing pads have a tendency to change readily over time, making suchpads difficult to use for a precise planarization treatment. Also,because the polishing pad is too flexible and deforms so as to followthe surface shape of the substrate being polished, it is difficult toobtain a high planarization performance (the ability to render thesubstrate being polished flat). In addition, the fibers have a finenessof 2 to 10 dtex and are thus large, making it difficult to avoid localstress concentration.

In such nonwoven fabric-type polishing pads, there has come to be known,more recently, a nonwoven fabric-type polishing pad which is obtained byusing a nonwoven fabric formed of bundles of ultrafine fibers, which isintended to achieve a higher planarization performance (e.g., see PatentDocuments 15 to 18). Specifically, Patent Document 15 describes apolishing pad in the form of a sheet composed of both a nonwoven fabricformed of entangled bundles of ultrafine polyester fibers having anaverage fineness of from 0.0001 to 0.01 dtex and a polymeric elastomermade primarily of a polyurethane present in spaces at the interior ofthe nonwoven fabric. This publication states that a polishing treatmentat a higher precision than before is achieved with such a polishing pad.

However, because the polishing pads like those described in PatentDocuments 15 to 18 make use of a nonwoven fabric obtained byneedlepunching ultrafine staple fibers having a low fineness, such padshave a low apparent density and a high void volume. Hence, only softpolishing pads with low stiffness can be obtained. Because thesepolishing pads deform so as to follow the surface shape, a sufficientlyhigh planarization performance cannot be achieved.

Also, none of these documents provide details concerning the polymericelastomer used in such nonwoven fabric-type polishing pads. Nor do thesedocuments sufficiently describe the stability of the polishing pads overtime.

-   Patent Document 1: Japanese Patent Application Laid-open No.    2000-178374-   Patent Document 2: Japanese Patent Application Laid-open No.    2000-248034-   Patent Document 3: Japanese Patent Application Laid-open No.    2001-89548-   Patent Document 4: Japanese Patent Application Laid-open No.    H11-322878-   Patent Document 5: Japanese Patent Application Laid-open No.    2002-9026-   Patent Document 6: Japanese Patent Application Laid-open No.    H11-99479-   Patent Document 7: Japanese Patent Application Laid-open No.    2005-212055-   Patent Document 8: Japanese Patent Application Laid-open No.    H3-234475-   Patent Document 9: Japanese Patent Application Laid-open No.    H10-128674-   Patent Document 10: Japanese Patent Application Laid-open No.    2004-311731-   Patent Document 11: Japanese Patent Application Laid-open No.    H10-225864-   Patent Document 12: Japanese Translation of PCT Application No.    2005-518286-   Patent Document 13: Japanese Patent Application Laid-open No.    2003-201676-   Patent Document 14: Japanese Patent Application Laid-open No.    2005-334997-   Patent Document 15: Japanese Patent Application Laid-open No.    2007-54910-   Patent Document 16: Japanese Patent Application Laid-open No.    2003-170347-   Patent Document 17: Japanese Patent Application Laid-open No.    2004-130395-   Patent Document 18: Japanese Patent Application Laid-open No.    2002-172555-   Non-Patent Document 1: M. Kashiwagi et al., “CMP no saiensu [The    science of CMP]”, Science Forum KK; Aug. 20, 1997, pp. 113-119

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a polishing padwhich is less likely to cause scratches and has both an excellentplanarization performance and polishing efficiency.

In one aspect, the invention relates to a polishing pad which comprisesan ultrafine fiber-entangled body formed of ultrafine fibers having anaverage fineness of 0.01 to 0.8 dtex, and a polymeric elastomer, whereinthe polymeric elastomer has a glass transition temperature of −10° C. orbelow, storage moduli at 23° C. and 50° C. of 90 to 900 MPa, and a waterabsorption ratio, when saturated with water at 50° C., of 0.2 to 5 mass%.

The objects, features, aspects and advantages of the inventions willbecome more apparent from the following detailed description.

MODE FOR CARRYING OUT THE INVENTION

Backing materials made of ultrafine fibers generally have a largesurface area and a low flexural modulus. For this reason, hitherto knownpolishing pads of a type obtained by impregnating a polymeric elastomerinto a nonwoven fabric composed of ultrafine fibers have a large contactsurface area with the substrate being polished, enabling to carry out asoft polishing. However, it has been possible to obtain in this way onlythe polishing pads having a low stiffness and falling short in terms oftheir planarizing characteristics and polishing stability over time.Because the voids in the nonwoven fabric become slurry reservoirs, thusgiving the nonwoven fabric a high ability to retain the abrasive slurry,the polishing rate is easily increased. Yet, given that voids accountfor more than one-half of the apparent volume, polishing pads of a typeobtained by impregnating hitherto known nonwoven fabrics with apolymeric elastomer, while capable of carrying out a highly efficientpolishing, have a low stiffness and thus leave something to be desiredin terms of the planarizing ability and the polishing stability overtime.

The inventors have arrived at the present invention after discoveringthat: (1) a polishing pad having a high stiffness can be obtained byusing an ultrafine fiber-entangled body of ultrafine fibers and apolymeric elastomer having a specific glass transition temperature,specific storage moduli and a specific water absorption ratio, and thestructure of such a polishing pad is maintained even during polishing,enhancing the polishing stability over time; (2) the fibers readily formfibrils at the surface of the polishing pad during polishing, therebyincreasing the contact surface area with the substrate being polishedand concurrently the wettability, which in turn increases the retentionof the abrasive slurry, resulting in an increased polishing rate; and(3) on account of the ultrafine fibers, the surface of the polishing padmakes soft contact to the substrate, minimizing stress concentrationduring polishing treatment, and making it less likely for scratches toform on the substrate being polished. The inventors have also foundthat, by setting the void volume of the polishing pad to 50% or more, itis possible to provide the pad with both an increased retention of theabrasive slurry and a high stiffness, which is particularly ideal forpolishing bare silicon wafers.

Thus, the polishing pad of the present embodiment is composed of anultrafine fiber-entangled body formed of ultrafine fibers having anaverage fineness of 0.01 to 0.8 dtex, and a polymeric elastomer, whereinthe polymeric elastomer has a glass transition temperature of −10° C. orbelow, storage moduli at 23° C. and 50° C. of 90 to 900 MPa, and a waterabsorption ratio, when saturated with water at 50° C. of 0.2 to 5 mass%.

The composition, method of manufacture and method of use of thepolishing pad according to the present embodiment are described below.

Composition of Polishing Pad

The ultrafine fiber-entangled body is formed of ultrafine fibers havingan average fineness in a range of from 0.01 to 0.8 dtex, and preferablyfrom 0.05 to 0.5 dtex. When the ultrafine fibers have an averagefineness below 0.01 dtex, the ultrafine fiber bundles near the surfaceof the polishing pad do not fully fibrillate, as a result of which theabrasive slurry retention will decrease, which may result in decreasesin the polishing efficiency and the polishing uniformity. On the otherhand, when the ultrafine fibers have an average fineness greater than0.8 dtex, the surface of the polishing pad becomes too coarse, loweringthe polishing rate. In addition, the stress in polishing with the fibersincreases, making scratches more likely to arise.

The ultrafine fiber-entangled body is composed of bundles of preferably5 to 70 ultrafine fibers, and more preferably 10 to 50 ultrafine fibers.When the number of ultrafine fibers collected into a bundle exceeds 70,the fibers near the surface of the polishing pad may not fullyfibrillate, as a result of which the retention of abrasive slurry maydecrease. On the other hand, when the number of ultrafine fiberscollected into a bundle is less than 5, the fineness becomessubstantially larger or the fiber density at the surface tends todecreases, which may make the surface of the polishing pad too coarseand lower the polishing rate. In addition, the stress in polishing withthe fibers increases, making scratches more likely to arise.

Examples of ultrafine fibers include aromatic polyester fibers formed ofpolyethylene terephthalate (PET), isophthalic acid-modified polyethyleneterephthalate, sulfoisophthalic acid-modified polyethyleneterephthalate, polybutylene terephthalate or polyhexamethyleneterephthalate; aliphatic polyester fibers formed of polylactic acid,polyethylene succinate, polybutylene succinate, polybutylene succinateadipate or polyhydroxybutyrate-polyhydroxyvalerate copolymer; polyamidefibers formed of polyamide 6, polyamide 66, polyamide 10, polyamide 11,polyamide 12 or polyamide 6-12; polyolefin fibers formed ofpolypropylene, polyethylene, polybutene, polymethylpentene or achlorinated polyolefin; modified polyvinyl alcohol fibers formed ofmodified polyvinyl alcohol containing 25 to 70 mol % of ethylene units;and elastomer fibers formed of a polyurethane elastomer, polyamideelastomer or polyester elastomer. These may be used alone or ascombinations of two or more types thereof. In view of enabling theformation of a compact, high-density ultrafine fiber-entangled body, itis especially preferable for the ultrafine fibers in the presentembodiment to be formed of polyester fibers.

Of the above ultrafine fibers, fibers which are formed of athermoplastic resin having a glass transition temperature (T_(g)) of atleast 50° C., and especially at least 60° C., and a water absorptionratio, when saturated with water at 50° C., of 0.2 to 2 mass %, arepreferred. When the glass transition temperature of the thermoplasticresin is in the above range, a higher stiffness can be maintained,thereby enabling the planarization performance to become even higher.Moreover, even during polishing, the stiffness does not decrease overtime, enabling to obtain a polishing pad having excellent polishingstability and polishing uniformity. From the standpoint of industrialproduction, the upper limit in the glass transition temperature,although not subject to any particular limitation, is preferably 300° C.or less, and more preferably 150° C. or less.

The ultrafine fibers of the present embodiment are preferably formed ofa thermoplastic resin having a water absorption ratio, when saturatedwith water at 50° C., of 0.2 to 2 mass %. In other words, it ispreferable that the thermoplastic resin used to form the ultrafinefibers has a water absorption ratio, when saturated with water at 50°C., of 0.2 to 2 mass %. By setting the water absorption ratio to atleast 0.2 mass %, the abrasive slurry is easily retained and thepolishing efficiency and polishing uniformity are readily enhanced. Bysetting the water absorption ratio to 2 mass % or less, the polishingpad does not absorb too much abrasive slurry, thereby better suppressinga decrease in the stiffness over time. In such cases, there can beobtained a polishing pad in which the decrease in planarizationperformance over time is suppressed and the polishing rate and polishinguniformity do not readily fluctuate. Owing to ready availability or goodmanufacturability in addition to the water absorption, it is preferablethat the thermoplastic resin from which the ultrafine fibers in theembodiment are formed is a polyester polymer, and especially asemi-aromatic polyester polymer in which an aromatic ingredient is usedas one of the starting components.

Illustrative examples of the thermoplastic resin include aromaticpolyester fibers formed of polyethylene terephthalate (PET; T_(g), 77°C.; water absorption ratio when saturated with water at 50° C. (referredto below as simply the “water absorption ratio”), 1 mass %), isophthalicacid-modified polyethylene terephthalate (T_(g), 67 to 77° C.; waterabsorption ratio, 1 masst %), sulfoisophthalic acid-modifiedpolyethylene terephthalate (T_(g), 67 to 77° C.; water absorption ratio,1 to 3 mass %), polybutylene naphthalate (T_(g), 85° C.; waterabsorption ratio, 1 mass %) or polyethylene naphthalate (T_(g), 124° C.;water absorption ratio, 1 mass %); and semi-aromatic polyamide fibersformed of a copolymeric polyamide of terephthalic acid with nonanedioland methyloctanediol (T_(g), 125 to 140° C.; water absorption ratio, 1to 3 mass %). PET and modified PET such as isophthalic acid-modified PETare especially preferred, for example, in that they undergo considerablecrimping in the below-described wet heat treatment operation in whichthe ultrafine fibers are formed from an entangled web sheet composed ofislands-in-the-sea type composite fibers, thus enabling a compact andhigh-density fiber-entangled body web of entangled fibers to be formed,in that the stiffness of the polishing sheet is easily increased, and inthat changes over time owing to moisture during polishing do not readilyarise.

The polishing pad according to the embodiment is preferably composed ofan ultrafine fiber-entangled body formed of preferably fiber bundlesinto which the above-described ultrafine fibers are collected together,and a polymeric elastomer.

The polymeric elastomers which may be used in the embodiment are notspecifically limited as long as they satisfy the below-described glasstransition temperature, storage moduli and water absorption ratioconditions. Illustrative examples of such polymeric elastomers includeelastomers which are composed of polyurethane resins, polyamide resins,(meth)acrylate resins, (meth)acrylate-styrene resins,(meth)acrylate-acrylonitrile resins, (meth)acrylate-olefin resins,(meth)acrylate-(hydrogenated) isoprene resins, (meth)acrylate-butadieneresins, styrene-butadiene resins, styrene-hydrogenated isoprene resins,acrylonitrile-butadiene resins, acrylonitrile-butadiene-styrene resins,vinyl acetate resins. (meth)acrylate-vinyl acetate resins,ethylene-vinyl acetate resins, ethylene-olefin resins, silicone resins,fluororesins and polyester resins.

As the polymeric elastomer of the embodiment, hydrogen-bonding polymericelastomers are preferred because of their good ability to have ultrafinefibers converge as bundles and to restrain and bind the ultrafine fiberbundles. Examples of resins which form the hydrogen-bonding polymericelastomers include polymeric elastomer resins that crystallize oraggregate under hydrogen bonding, such as polyurethane resins, polyamideresins, polyvinyl alcohol resins. The hydrogen-bonding polymericelastomer has a high adhesion, a high fiber bundle restraining ability,and minimizes the loss of fibers.

The polymeric elastomer used in the embodiment has a glass transitiontemperature of −10° C. or below. At a glass transition temperaturehigher than −10° C., the polymeric elastomer becomes brittle, as aresult of which the polymeric elastomer sheds more readily duringpolishing, which tends to give rise to scratching. In addition, theultrafine fiber bundle convergence owing to the polymeric elastomerbecomes weaker, which tends to result in a decline in stability overtime during polishing. The glass transition temperature is preferably−15° C. or below. Although there is no particular lower limit, in termsavailability and other considerations, a lower limit of −100° C. orabove is preferred. The glass transition temperature is computed fromthe peak temperature of the loss modulus in the tensile mode duringmeasurement of the dynamic viscoelasticity. Because the glass transitiontemperature is dependent on the peak temperature of a dispersion by thepolymeric elastomer, it is preferable to suitably select the ingredientsmaking up the polymeric elastomer so as to set the glass transitiontemperature of the polymeric elastomer to −10° C. or below. For example,when a polyurethane resin is used as the polymeric elastomer, thecomposition of the polyols serving as the soft component and therelative proportions of the hard component (isocyanate component andchain extender component) and the soft component are selected in such away as to set the glass transition temperature to −10° C. or below.Specifically, it is desirable to select a polyol having a glasstransition temperature of −10° C. or below, preferably −20° C. or below,and to select a composition in which the mass ratio of the polyolcomponent within the polyurethane is at least 30 wt %, and preferably atleast 40 wt %.

The polymeric elastomer used in the embodiment has storage moduli at 23°C. and 50° C. of in a range from 90 to 900 MPa. The storage moduli ofpolyurethanes at 23° C. and 50° C. are generally less than 90 MPa.However, at storage moduli at 23° C. and 50° C. of less than 90 MPa, thepolymeric elastomer which restrains the fiber bundles readily deforms,resulting in inadequate pad stiffness during polishing and thus loweringthe planarizing ability. Moreover, the polymeric elastomer swells morereadily due to the slurry, etc. during polishing, as a result of whichthe stability over time tends to decline. On the other hand, when thestorage moduli at 23° C. and 50° C. exceed 900 MPa, the polymericelastomer becomes brittle, as a result of which the polymeric elastomersheds more readily during polishing, which tends to give rise toscratching. In addition, the ultrafine fiber bundle convergencedecreases, as a result of which the stability over time during polishingreadily worsens. The storage moduli at 23° C. and 50° C. are preferablyfrom 200 to 800 MPa. Because the storage moduli of the polymericelastomer are dependent on the composition of the polymeric elastomer,that is, on the respective elastic moduli of and the weight ratiobetween the hard component and the soft component making up thepolymeric elastomer, it is preferable to select the composition of andthe weight ratio between the hard component and the soft component insuch a way as to set the storage moduli in the above range.

For example, when a polyurethane resin is used as the polymericelastomer, illustrative examples of the soft component (polyolcomponent) include polyether polyols such as polyethylene glycol,polypropylene glycol, polytetramethylene glycol andpoly(methyltetramethylene glycol), and copolymers thereof; polyesterpolyols such as polybutylene adipate diol, polybutylene sebacate diol,polyhexamethylene adipate diol, poly(3-methyl-1,5-pentylene adipate)diol, poly(3-methyl-1,5-pentylene sebacate) diol, isophthalic acidcopolymeric polyol, terephthalic acid copolymeric polyol, cyclohexanolcopolymeric polyol and polycaprolactone diol, and copolymers thereof;polycarbonate polyols such as polyhexamethylene carbonate diol,poly(3-methyl-1,5-pentylene carbonate) diol, polypentamethylenecarbonate diol, polytetramethylene carbonate diol,poly(methyl-1,8-octamethylene carbonate) diol, polynonane methylenecarbonate diol and polycyclohexane carbonate, and copolymers thereof;and polyester carbonate polyols. Also, if necessary, a polyfunctionalalcohol such as a trifunctional alcohol (e.g., trimethylolpropane) or atetrafunctional alcohol (e.g., pentaerythritol); or a short-chainalcohol such as ethylene glycol, propylene glycol, 1,4-butanediol or1,6-hexanediol, may be concomitantly used. These may be used singly oras combinations of two or more thereof. In particular, it is preferableto include a polycarbonate polyol such as an alicyclic polycarbonatepolyol, a linear polycarbonate polyol or a branched polycarbonate polyolin an amount of 60 to 100 mass % of the overall polyol component, and toinclude especially a noncrystalline polycarbonate polyol having amelting point of 0° C. or below in an amount of 60 to 100 mass % of theoverall polyol component, because the stability over time duringpolishing is good on account of high resistance to the slurry used inpolishing and because the water absorption and the storage moduli caneasily be set within the above range of the embodiment.

Moreover, in order to set the storage moduli at 23° C. and 50° C. in arange of from 90 to 900 MPa, it is preferable to select a polyol havinga glass transition temperature of −10° C. or below, and preferably −20°C. or below. Illustrative examples include the above-mentioned branchedpolycarbonate polyols; polyether polyols such as polypropylene glycol,polytetramethylene glycol and poly(methyltetramethylene glycol), andcopolymers thereof; polyester polyols such as polybutylene sebacatediol, poly(3-methyl-1,5-pentylene adipate) diol,poly(3-methyl-1,5-pentylene sebacate) diol and polycaprolactone diol,and copolymers thereof; polycarbonate polyols such aspoly(3-methyl-1,5-pentylene carbonate) diol andpoly(methyl-1,8-octamethylene carbonate) diol, and copolymers thereof;and polyester carbonate polyols. In addition to the above polyols,further examples include those polyols whose glass transitiontemperature can be set to −10° C. or below by copolymerization.

Because polyurethane resins containing polyalkylene glycol groups withup to 5 carbons, and especially up to 3 carbons, have an especially goodwettability to water, it is preferable to use a polyurethane resincontaining from about 0.1 to about 10 mass % of such polyalkylene glycolgroups.

By using a soft component (polyol component) having a glass transitiontemperature of −10° C. or below and thereby setting the glass transitiontemperature of the polyurethane to −10° C. or below, and by selectingsuch a polyol component and adjusting the mass ratio of the polyolcomponent in the polyurethane, the storage moduli of the polyurethane at23° C. and 50° C. can be set in a range of from 90 to 900 MPa.

When a polyurethane resin is used as the polymeric elastomer, theisocyanate component used in the hard component (isocyanate componentand chain extender component) may be a non-yellowing diisocyanate whichis an aliphatic or alicyclic diisocyanate, such as hexamethylenediisocyanate, isophorone diisocyanate, norbornene diisocyanate and4,4′-dicyclohexylmethane diisocanate; or an aromatic diisocyanate, suchas 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,4,4′-diphenylmethane diisocyanate and xylylene diisocyanatepolyurethane. If necessary, concomitant use may be made of apolyfunctional isocyanate such as a trifunctional isocyanate or atetrafunctional isocyanate. These may be used singly or as combinationsof two or more thereof. Of these, 4,4′-dicyclohexylmethane diisocyanate,2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,4,4′-diphenylmethane diisocyanate and xylylene diisocyanate arepreferred because they have a high adhesion to ultrafine fibers andincrease the ultrafine fiber bundle convergence, thereby enabling apolishing pad having a high hardness to be obtained.

As the other hard component (chain extender component), a hard componentwhich has a high cohesiveness and a high elastic modulus and is composedof a combination of a short-chain polyol, such as a diol (e.g., ethyleneglycol, propylene glycol, 1,4-butanediol,1,4-bis(p-hydroxyethoxy)benzene, 1,4-cyclohexane diol), triol (e.g.,trimethylolpropane), pentaol (e.g., pentaerythritol) or aminoalcohol(e.g., aminoethyl alcohol, aminopropyl alcohol), with a short-chainpolyamine, such as a diamine (e.g., hydrazine, ethylenediamine,propylenediamine, hexamethylenediamine, xylylenediamine,isophoronediamine, piperazine and derivatives thereof, adipic aciddihydrazide, isophthalic acid dihydrazide), triamine (e.g.,diethylenetriamine) or tetramine (e.g., triethylenetetramine), may beselected for use as the chain extender component. Examples which may beused together with the chain extender at the time of the chain-extendingreaction include a monoamine (e.g., ethylamine, propylamine,butylamine), a carboxyl group-containing monoamine compound (e.g.,4-aminobutanoic acid, 6-aminohexanoic acid), or a monool (e.g.,methanol, ethanol, propanol, butanol). By concomitantly using a carboxylgroup-containing diol such as 2,2-bis(hydroxymethyl)propionic acid,2,2-bis(hydroxymethyl)butanoic acid or 2,2-bis(hydroxymethyl)valericacid, ionic groups such as the carboxylic groups can be introduced ontothe skeleton of the polyurethane elastomer, making it possible tofurther enhance the wettability to water.

From the standpoint of setting the storage moduli of the polyurethane at23° C. and 50° C. within a range of from 90 to 900 MPa, the proportionof the soft component (polyol component) is set to preferably from 40 to65 mass %, and more preferably from 45 to 60 mass %. At an amount of thesoft component below 40 mass %, the temperature dependence of thestorage moduli at 23° C. and 50° C. becomes higher, making it difficultto achieve a range of from 90 to 900 MPa. On the other hand, if theamount of the soft component exceeds 65 wt %, the storage moduli tend tofall below 90 MPa.

From the standpoint of more easily increasing the storage moduli of thepolyurethane, it is especially preferable for the soft component to be apolycarbonate-type polyol, such as a branched polycarbonate polyol;poly(3-methyl-1,5-pentylene carbonate) diol orpoly(methyl-1,8-octamethylene carbonate) diol; or a polycarbonate polyolobtained by copolymerizing such polycarbonate polyols aspoly(3-methyl-1,5-pentylene carbonate) diol,poly(methyl-1,8-octamethylene carbonate) diol, polyhexamethylenecarbonate diol, polypentamethylene carbonate diol, polytetramethylenecarbonate diol, polynonanemethylene carbonate diol and polycyclohexanecarbonate.

Moreover, it is preferable for the polymeric elastomer in the presentembodiment to have a ratio of the storage modulus at 23° C. to thestorage modulus at 50° C. (storage modulus at 23° C./storage modulus at50° C.) of 4 or less. By setting the ratio of the storage modulus at 23°C. to the storage modulus at 50° C. (storage modulus at 23° C./storagemodulus at 50° C.) to 4 or less, the storage moduli are less subject tochange even when temperature changes arise during polishing, therebyenhancing the stability over time during polishing. It is especiallypreferable to set the ratio of the storage modulus at 23° C. to thestorage modulus at 50° C. (storage modulus at 23° C./storage modulus at50° C.) to 3 or less. The lower limit value is not subject to anyparticular limitation; however, in order for the storage modulus to beless subject to change due to the temperature during polishing, a valueof ⅓ or more is preferred.

The foregoing range can be achieved by suitably adjusting the softcomponent and the hard component so as to set the storage moduli in theabove-described range.

For example, in cases where a polyurethane resin is employed as thepolymeric elastomer, it is desirable to use a soft component (polyolcomponent) having a glass transition temperature of −10° C. or below soas to set the glass transition temperature of the polyurethane to −10°C., to select as the hard components (isocyanate component and chainextender component) an alicyclic diisocyanate or an aromaticdiisocyanate, and a chain extender component having a high cohesivenessand a high elastic modulus which is obtained from a combination of ashort-chain polyol (examples of which include diols, triols andpentaols) with a short-chain polyamine (examples of which includediamines, triamines and tetramines), and to set the ratio of the softcomponent at preferably from 40 to 65 mass %, and more preferably from45 to 60 mass %. Also, a polycarbonate polyol is preferred as the softcomponent of the polyurethane because it makes the elastic modulus ofthe polyurethane easy to increase.

In order to adjust, for example, the performance or manufacturability ofthe polishing pad, two or more polymeric elastomers may be included. Thestorage moduli at 23° C. to 50° C. of the polymeric elastomer in such acase can be theoretically calculated as the sum of the values obtainedby multiplying the storage modulus of each polymeric elastomer by themass fraction thereof.

Moreover, the polymeric elastomer of the present embodiment has a waterabsorption ratio, when saturated with water at 50° C., of 0.2 to 5 mass%. At a water absorption ratio below 0.2 mass %, retaining the abrasiveslurry becomes difficult, as a result of which the polishing efficiencyand the polishing uniformity tend to decline. At above 5 mass %, thepolymeric elastomer which restrains the fiber bundles absorbs water andsoftens, as a result of which the change over time during polishingtends to increase. Moreover, it is preferable for the water absorptionratio when saturated with water at 50° C. to be in a range of from 0.5to 3 mass %. When the water absorption ratio of the polymeric elastomeris in such a range, a high wettability of the polishing pad by theabrasive slurry is maintained, in addition to which a decline over timein the stiffness can be better suppressed. This enables a high polishingrate, polishing uniformity and polishing stability to be maintained.

The water absorption ratio of polymeric elastomer, which will besubsequently described in greater detail, refers herein to the waterabsorption ratio when a polymeric elastomer film that has been subjectedto drying treatment is immersed in room-temperature water and allowed toswell to saturation. The water absorption ratio in cases where two ormore types of polymeric elastomer are included can be theoreticallycalculated as the sum of the values obtained by multiplying the waterabsorption ratio of each polymeric elastomer by the mass fractionthereof.

The polymeric elastomer having such a water absorption ratio can beobtained, for example, by adjusting the composition and crosslinkdensity of the polymers making up the polymeric elastomer, introducinghydrophilic functional groups, and selecting the amounts thereof.

For example, the water absorption ratio and hydrophilicity can beadjusted by introducing to the polymeric elastomer at least one type ofhydrophilic group selected from the group consisting of carboxylicgroups, sulfonic acid groups, and polyalkylene glycol groups having 3 orfewer carbons. In this way, the wettability of the polishing pad by theabrasive slurry can be increased. Such hydrophilic groups may beintroduced onto the polymeric elastomer by the copolymerization of amonomer having hydrophilic groups as a monomer component duringproduction of the polymeric elastomer. Setting the copolymerizationratio of such a monomer component having hydrophilic groups at from 0.1to 10 mass %, and especially from 0.5 to 5 wt %, is preferable from thestandpoint of minimizing swelling and softening due to water absorptionand increasing the water absorption ratio and wettability.

The polymeric elastomers may be used singly or as combinations of two ormore thereof. Of such polymeric elastomers, a polyurethane resin ispreferred in that it has excellent adhesive properties for packingultrafine fibers into bundles or for restraining and binding togetherthe fiber bundles, in addition to which it increases the hardness of thepolishing pad and has an excellent stability over time during polishing.Also, the polyurethane resin having at least one type of hydrophilicgroup selected from the group consisting of carboxylic groups, sulfonicacid groups and polyalkylene glycol groups of 3 or fewer carbons isdesirable from the standpoint of the polishing pad stiffness,wettability and stability over time during polishing.

In cases where the polymeric elastomer is the polyurethane resin,specific examples of carboxylic groups include the carboxylic groups of2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butanoicacid and 2,2-bis(hydroxymethyl)valeric acid. By concomitantly using, forexample, these diols having the carboxylic groups, it is possible tointroduce carboxylic groups onto the skeleton of the polyurethaneelastomer. Illustrative examples of polyalkylene glycol groups having 3or fewer carbons include polyethylene glycol, polypropylene glycol andcopolymers thereof. Although polyurethane resins having at least onetype of hydrophilic group selected from among carboxylic groups,sulfonic acid groups and polyalkylene glycol groups of 3 or fewercarbons do have the advantage of an enhanced wettability, the waterabsorption ratio tends to rise and is generally from 5 to 15 mass %.Therefore, in order to set the water absorption ratio in the range of0.2 to 5 mass % in the present embodiment, it is desirable to set theamount of at least one hydrophilic group selected from the groupconsisting of carboxylic groups, sulfonic acid groups and polyalkyleneglycol groups of 3 or fewer carbons to preferably from 0.1 to 10 mass %,and more preferably from 0.5 to 5 mass %. In addition, it is preferableto use as the polyol a component having low water absorption, such asthe above-described polyester polyol or polycarbonate polyol.

For example, in cases where the polymeric elastomer is a polyurethaneresin obtained by using as the polyol component a noncrystallinepolycarbonate diol together with a carboxylic group-containing diol, andusing an alicyclic diisocyanate as the diisocyanate component, the useof such a polymeric elastomer is preferred because of the ease ofsetting the glass transition temperature of the polymeric elastomer to−10° C. or below, setting the storage moduli at 23° C. and 50° C. tofrom 90 to 900 MPa, and setting the water absorption ratio whensaturated with water at 50° C. to from 0.2 to 5 mass %.

The hard components (isocyanate component and chain extender component)of the polyurethane resin used in the embodiment may be, for example,the above-described isocyanate component and the above-described chainextender component having a high cohesiveness. Also, the ratio of thesoft component (polyol component) is preferably set to 65 mass % orless, and more preferably 60 mass % or less. At an amount of the softcomponent in excess of 65 wt %, the water absorption ratio tends tobecome high. In cases where the polymeric elastomer is an aqueouspolyurethane, to achieve a water absorption ratio of from 0.2 to 5 mass%, it is preferable for the aqueous polyurethane to have an averageparticle size of from 0.01 to 0.2 μm. At an average particle size ofless than 0.01 μm or more than 0.2 μm, the water absorption ratio willtend to exceed 5 mass %.

In cases where the polymeric elastomer is a polyurethane resin, tocontrol the water absorption ratio and the storage moduli, it ispreferable also to form a crosslinked structure by adding a crosslinkingagent having in the molecule two or more functional groups capable ofreacting with the functional groups in the above-mentioned monomer unitswhich form the polyurethane, or by adding a self-crosslinking compoundsuch as a polyisocyanate compound or a polyfunctional blockisocyanate-type compound.

Examples of combinations of the functional group in the above-mentionedmonomer unit with the functional group in the crosslinking agent includea carboxylic group with an oxazoline group, a carboxylic group with acarbodiimide group, a carboxylic group with an epoxy group, a carboxylicgroup with a cyclocarbonate group, a carboxylic group with an aziridinegroup, and a carbonyl group with a hydrazine derivative or a hydrazidederivative. Of these, combinations of the monomer unit having thecarboxylic group with the crosslinking agent having the oxazoline group,the carbodiimide group or the epoxy group, combinations of the monomerunit having the hydroxyl group or the amino group with the crosslinkingagent having the block isocyanate group, and combinations of the monomerunit having the carbonyl group with the hydrazine derivative or thehydrazide derivative are especially preferred on account of the ease ofcrosslinkage formation and the excellent stiffness and wear resistanceof the polishing pad thereby obtained. Formation of the crosslinkedstructure in a heat treatment step following impregnation of thefiber-entangled body with an aqueous liquid of the polyurethane resin ispreferred from the standpoint of maintaining the stability of theaqueous liquid of the polymeric elastomer. Of the above, thecarbodiimide group and/or the oxazoline group are especially preferredon account of their excellent crosslinking ability and the pot life ofthe aqueous liquid, and also because these pose no problems in terms ofsafety. Illustrative examples of crosslinking agents having thecarbodiimide group include water-dispersible carbodiimide compounds suchas Carbodilite E-01, Carbodilite E-02 and Carbodilite V-02, allavailable from Nisshinbo Industries, Inc. Illustrative examples ofcrosslinking agents having the oxazoline group include water-dispersibleoxazoline compounds such as Epocros K-2010E, Epocros K-2020E and EpocrosWS-500, all available from Nippon Syokubai Co., Ltd. The amount of thecrosslinking agent included in the polyurethane resin, expressed interms of the active ingredient of the crosslinking agent with respect tothe polyurethane resin, is preferably from 1 to 20 mass %, and morepreferably from 1.5 to 10 mass %.

In order to increase adhesion with the ultrafine fibers and increase therigidity of the fiber bundles, and in order to facilitate adjustments,such as setting the glass transition temperature to −10° C. or below,setting the storage moduli at 23° C. and 50° C. in a range of 90 to 900MPa, and setting the water absorption ratio when saturated with water at50° C. to 0.2 to 5 mass %, the content of the polyol component in thepolyurethane resin is preferably 65 mass % or less, and more preferably60 mass % or less. Also, the content of at least 40 mass %, andespecially at least 45 mass %, is preferred in that a suitableelasticity is imparted, making it possible to minimize the occurrence ofscratches.

The polyurethane resin may additionally include, within ranges that donot compromise the advantageous effects of the invention: penetratingagents, foam inhibitors, lubricants, water repellents, oil repellents,thickeners, bulking agents, curing accelerators, antioxidants,ultraviolet absorbers, mold inhibitors, blowing agents, water-solublepolymeric compounds such as polyvinyl alcohol and carboxymethylcellulose, dyes, pigments, and inorganic fine particles.

Preferably, the polymeric elastomer is present inside ultrafine fiberbundles of from 5 to 70 ultrafine fibers having an average fineness of0.01 to 0.8 dtex which make up the ultrafine fiber-entangled body. Theultrafine fibers converge as bundles under the effect of the polymericelastomer present inside the ultrafine fiber bundles. Owing to theconvergence of the ultrafine fibers, a part or all of the interior ofthe fiber bundle converges as a bundle, in addition to which the bundleof ultrafine fibers is restrained. The convergence of the ultrafinefibers as a bundle, together with the restraint of the fiber bundle,increases the stiffness of the polishing pad, which is advantageous fromthe standpoint of enhancing the planarizing performance, the polishinguniformity and the stability over time.

A volumetric ratio of a portion excluding voids in the polishing pad(also referred to below as the filling ratio of the polishing pad) ispreferably in a range of from 40 to 95 wt %. That is, the presence ofthe voids such that the void volume is in a range of from 5 to 60% ispreferable both for a suitable stiffness of the polishing pad and forslurry retention by the polishing pad.

In this case, the void volume in the polymeric elastomer-impregnatedpolishing pad of 50% or more is desirable because slurry retention,suitable stiffness and moreover cushionability are concurrentlyachieved, which is excellent for polishing bare silicon wafers. An upperlimit in this case of 70% or less is desirable because this results in agood polishing rate and flatness in rough polishing such as bare siliconwafer polishing.

From the standpoint of enhancing slurry retention, it is more desirablefor some of the voids to form continuous pores which affordcommunication with the interior of the polishing pad.

Moreover, the polymeric elastomer is preferably an aqueous polyurethanebecause of the good wettability to abrasive slurry, and the aqueouspolyurethane preferably has an average particle size of 0.01 to 0.2 μm.At an average particle size of at least 0.01 μm, the water resistance isgood, resulting in an excellent stability over time during polishing. Anaverage particle size of 0.2 μm or less enhances the fiber bundlerestraining strength, confers good planarizing properties, and increasesthe pad life during polishing, providing good stability over time. Toadjust the above particle size, it is preferable, for example, that thepolymeric elastomer includes at least one type of hydrophilic groupselected from the group consisting of carboxylic groups, sulfonic acidgroups and polyalkylene glycol groups having 3 or fewer carbons.

The mass ratio of the ultrafine fiber-entangled body to the polymericelastomer (ultrafine fiber-entangled body/polymeric elastomer) ispreferably from 55/45 to 95/5. A mass ratio for the ultrafinefiber-entangled body of 55% or more has a good effect for the stabilityover time during polishing, and tends to enhance the polishingefficiency. At a mass ratio for the ultrafine fiber-entangled body of95% or less, the restraining strength of the polymeric elastomer at theinterior of the fiber bundles is maintained, resulting in excellentplanarizing properties and little pad wear during polishing. The massratio of the ultrafine fiber-entangled body to the polymeric elastomeris most preferably in a range of from 60)/40 to 90/10.

To maintain a good slurry retention and maintain a high stiffness, theapparent density of the polishing pad of the embodiment is preferably ina range of 0.4 to 1.2 g/cm³, and more preferably from 0.5 to 1.0 g/cm³.In a use for bare silicon wafer polishing, to achieve both an enhancedpolishing rate and planarity, the apparent density is preferably from0.3 to 0.75 g/cm³, and more preferably from 0.4 to 0.65 g/cm³.

In the present embodiment, the average length of the ultrafine fiberbundles is not subject to any particular limitation. However, having theaverage length be at least 100 mm, and preferably at least 200 mm, isdesirable in that the fiber density can be easily increased, thestiffness of the polishing pad can be easily increased, and the loss offibers can be suppressed. If the length of the fiber bundles is tooshort, a higher fiber density will be difficult to achieve, in additionto which a sufficiently high stiffness is not attained, and ultrafinefibers will have a greater tendency to shed during polishing. The upperlimit is not subject to any particular limitation. For example, when anultrafine fiber-entangled body from a nonwoven fabric manufactured bythe below-described spunbonding process is included, fibers havinglengths of several meters, several hundreds of meters, severalkilometers or more may be included as far as they are not physicallycut.

The polishing pad of the embodiment preferably has a compositeconstruction obtained by filling the polymeric elastomer into theultrafine fiber-entangled body.

In the polishing pad of the embodiment, having the polymeric elastomerpresent at the interior of the ultrafine fiber bundles is preferable forincreasing the stiffness of the polishing pad, and it is more preferablefor the ultrafine fibers which make up the ultrafine fiber bundles to bebundled under the effect of the polymeric elastomer. By having theultrafine fibers bundled in this way, the stiffness of the polishing padis further increased. Bundling the ultrafine fibers makes it difficultfor the individual fibers to move, thereby increasing the stiffness ofthe polishing pad and enabling a high planarizing performance to bereadily achieved. Also, the loss of fibers decreases and the aggregationof abrasive particles at fibers that have been shed can be prevented,thereby minimizing the occurrence of scratches. As used herein, thefeature that the ultrafine fibers are bundled refers to a state where alarge portion of the ultrafine fibers present at the interior of theultrafine fiber bundles (preferably at least 10%, more preferably atleast 20%, even more preferably at least 50%, and most preferably atleast 60%, of the number of fibers) are bonded and restrained by thepolymeric elastomer present at the interior of the ultrafine fiberbundles.

Moreover, it is also preferable for a plurality of ultrafine fiberbundles to be mutually bonded by the polymeric elastomer present outsideof the ultrafine fiber bundles, and to exist in a bulk state. By bindingtogether the ultrafine fiber bundles in this way, the shape stability ofthe polishing pad is enhanced, thus increasing the polishing stability.

The bundled and restrained state of the ultrafine fibers and the boundstate between the ultrafine fiber bundles can be confirmed from electronmicrographs of cross-sections of the polishing pad.

The polymeric elastomer which bundles the ultrafine fibers and thepolymeric elastomer which binds together the ultrafine fiber bundles ispreferably a nonporous elastomer. Here, “nonporous” signifies a state inwhich there are substantially no voids (closed pores) as would exist inporous or sponge-like (referred to below simply as “porous”) polymericelastomers. Concretely, this means, for example, that it is not apolymeric elastomer having many tiny pores as would be obtained bycoagulating a solvent-based polyurethane. In cases where the polymericelastomer for bundling or binding is nonporous, because the polishingstability increases and slurry debris and pad debris do not readilyaccumulate in the voids during polishing, the polishing pad is lesssubject to wear, enabling a high polishing rate to be maintained for anextended period of time. In addition, because the adhesive strength withrespect to the ultrafine fibers is high, the occurrence of scratchesthat arise from the shedding of fibers can be suppressed. Moreover,because a higher stiffness can be achieved, a polishing pad having anexcellent planarization performance is obtained.

The polishing pad in the present embodiment preferably has a waterabsorption ratio when swollen to saturation with 50° C. water, ofpreferably 10 to 80 mass %, and more preferably 15 to 70 mass %. At sucha water absorption ratio of at least 10 mass %, the abrasive slurry iseasily retained, as a result of which the polishing rate increases andthe polishing uniformity tends to improve. At such a water absorptionratio of 80 mass % or less, a high polishing rate is achieved. Moreover,because properties such as hardness do not readily change duringpolishing, the stability over time in the planarization performancetends to be outstanding.

By subjecting the polishing pad of the present embodiment to apad-flattening treatment by buffing or the like, a seasoning treatment(conditioning treatment) using a pad dressing such as a diamond prior topolishing, or a dressing treatment at the time of polishing, theultrafine fiber bundles present near the surface can be separated orfibrillated, enabling the ultrafine fibers to be formed at the surfaceof the polishing pad. The fiber density of the ultrafine fibers at thepolishing pad surface is preferably at least 600 fibers/mm², morepreferably at least 1,000 fibers/mm², and most preferably at least 2,000fibers/mm². If the fiber density is too low, the retention of theabrasive slurry will tend to be insufficient. From the standpoint ofmanufacturability, the upper limit in the fiber density, although notsubject to any particular limitation, is about 1,000,000 fibers/mm². Theultrafine fibers at the surface of the polishing pad may or may notstand upright. In cases where the ultrafine fibers stand upright, thesurface of the polishing pad becomes softer, further increasing thescratch-reducing effect. On the other hand, in cases where the degree ofuprightness of the ultrafine fibers is low, this is advantageous forapplications in which importance is placed on the micro-flatness. It ispreferable in this way to suitably select the surface state according tothe intended application.

Method for Manufacturing the Polishing Pad

Next, an example of a method for manufacturing the polishing pad of thepresent embodiment is described in detail.

The polishing pad of the embodiment can be obtained by a manufacturingmethod which includes, for example, a web fabricating step whichfabricates a filament web composed of islands-in-the-sea type compositefibers obtained by melt spinning a water-soluble thermoplastic resin anda water-insoluble thermoplastic resin; a web entangling step which formsan entangled web sheet by stacking together a plurality of the filamentwebs and entangling the webs; a wet heat shrinkage treatment step whichshrinks the entangled web sheet to a surface area shrinkage ratio of atleast 30% by subjecting the sheet to wet heat shrinkage; an ultrafinefiber-entangled body-forming step which forms an ultrafinefiber-entangled body composed of ultrafine fibers by dissolving thewater-soluble thermoplastic resin within the entangled web sheet in hotwater; and a polymeric elastomer filling step which impregnates theultrafine fiber-entangled body with an aqueous liquid of a polymericelastomer and dry-coagulates the elastomer.

In the above manufacturing method, by passing through the step whereinthe entangled web sheet containing filaments is subjected to wet heatshrinkage, the entangled web sheet can be shrunk to a considerabledegree compared with a case in which an entangled web sheet containingstaple fibers is subjected to wet heat shrinkage, thereby increasing thefiber density of the ultrafine fibers. Moreover, by dissolving andextracting the water-soluble thermoplastic resin in the entangled websheet, an ultrafine fiber-entangled body composed of ultrafine fiberbundles is formed. At this time, voids are formed in the areas where thewater-soluble thermoplastic resin has been dissolved and extracted.Next, by thoroughly impregnating a high-concentration aqueous liquid ofthe polymeric elastomer into these voids and by dry-coagulating theelastomer, the ultrafine fibers making up the ultrafine fiber bundlesconverge together, and the ultrafine fiber bundles also mutuallyconverge. In this way, there can be obtained the polishing pad which hasa high fiber density, a low void volume and, because the ultrafinefibers have been made to converge as bundles, a high stiffness.

By controlling the shrinkage treatment and adjusting the amount ofpolymeric elastomer impregnated into the voids so as to set the voidvolume of the polishing pad to 50% or more, the polishing pad suitablefor use on bare silicon wafers can be obtained, in which the polishingpad has an appropriate stiffness and both an improved abrasive-slurryretention and an improved cushionability.

Each of the manufacturing steps is described below in greater detail.

(1) Web Fabricating Step

In this step, first a filament web composed of islands-in-the-sea typecomposite fibers obtained by melt spinning a water-soluble thermoplasticresin and a water-insoluble thermoplastic resin is produced.

The islands-in-the-sea type composite fibers are obtained byrespectively melt spinning a water-soluble thermoplastic resin and awater-insoluble thermoplastic resin having a low compatibility with thewater-soluble thermoplastic resin, then by combining the two. Ultrafinefibers are then formed by dissolving and removing, or decomposing andremoving, the water-soluble thermoplastic resin from theislands-in-the-sea type composite fibers. From an industrial standpoint,it is preferable for the size of the islands-in-the-sea type compositefibers to be from 0.5 to 3 dtex.

In the embodiment, islands-in-the-sea type composite fibers aredescribed in detail as the composite fibers employed to form ultrafinefibers. However, in place of islands-in-the-sea type fibers, other knownultrafine fiber-generating fibers such as fibers having a multilayerlaminated cross-section can be also used.

As the water-soluble thermoplastic resin, a thermoplastic resin whichcan be dissolved and removed or decomposed and removed using, forexample, water, an alkaline aqueous solution or an acidic aqueoussolution, and which is melt-spinnable may be advantageously used.Examples of such water-soluble thermoplastic resins include polyvinylalcohol resins (PVA resins) such as polyvinyl alcohol and polyvinylalcohol copolymers; modified polyesters containing polyethylene glycoland/or an alkali metal salt of sulfonic acid as the copolymerizingingredients; and polyethylene oxide. Of these, the use of a PVA resin isespecially preferred for the following reasons.

When islands-in-the-sea type composite fibers using a PVA resin as thewater-soluble thermoplastic resin component are employed, the ultrafinefibers formed by dissolving the PVA resin undergo a considerable degreeof crimping. As a result, an ultrafine fiber-entangled body having ahigher fiber density is obtained. Alternatively, in cases whereislands-in-the-sea type composite fibers in which a PVA resin serves asthe water-soluble thermoplastic resin component are used, when the PVAresin is dissolved, because the formed ultrafine fibers and thepolymeric elastomer substantially do not decompose or dissolve, thephysical properties of the ultrafine fibers and the polymeric elastomerdo not readily decline. Moreover, the burden on the environment is alsolow.

The PVA resin can be obtained by saponifying a copolymer in which vinylester units serve as a primary component. Illustrative examples of vinylmonomers for forming the vinyl ester units include vinyl acetate, vinylformate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate,vinyl stearate, vinyl benzoate, vinyl pivalate and vinyl versatate.These may be used singly or as combinations of two or more thereof. Ofthese, vinyl acetate is preferred from an industrial standpoint.

The PVA resin may be a homo-PVA composed only of vinyl ester units, ormay be a modified PVA containing as constituent units copolymerizablemonomer units other than vinyl ester units. In terms of the ability tocontrol the melt spinnability, the water solubility and the physicalproperties of the fibers, the modified PVA is more preferred.Illustrative examples of copolymerizable monomer units other than thevinyl ester units include α-olefins having 4 or fewer carbons, such asethylene, propylene, 1-butene and isobutene; and vinyl ethers such asmethyl vinyl ether, ethylene vinyl ether, n-propyl vinyl ether,isopropyl vinyl ether and n-butyl vinyl ether. The content ofcopolymerizable monomer units other than vinyl ester units is in a rangeof preferably from 1 to 20 mol %, more preferably from 4 to 15 mol %,and even more preferably from 6 to 13 mol %. Of these, anethylene-modified PVA containing from 4 to 15 mol %, and especially from6 to 13 mol %, of the ethylene units is preferred because the resultingislands-in-the-sea type composite fibers have higher physicalproperties.

From the standpoint of forming a stable islands-in-the-sea structure,exhibiting a melt viscosity with excellent melt spinning properties, andhaving a rapid dissolution rate during dissolution, it is desirable forthe PVA resin to have a viscosity-average degree of polymerization in arange of from 200 to 500, preferably from 230 to 470, and mostpreferably from 250 to 450. The above degree of polymerization ismeasured in general accordance with JIS-K6726. That is, theviscosity-average degree of polymerization is calculated according tothe following formula from the intrinsic viscosity [η] measured in 30°C. water after the PVA resin is re-saponified and purified.

Viscosity-average degree of polymerization P=([η]×103/8.29)(1/0.62)

The degree of saponification of the PVA resin is preferably from 90 to99.99 mol %, more preferably from 93 to 99.98 mol %, even morepreferably from 94 to 99.97 mol %, and most preferably from 96 to 99.96mol %. When the degree of saponification is in such a range, a PVA resinhaving an excellent water solubility, good thermal stability, excellentmelt spinnability and excellent biodegradability can be obtained.

From the standpoint of having excellent mechanical properties andthermal stability, and also from the standpoint of having an excellentmelt spinnability, it is desirable for the melting point of the abovePVA resin to be in a range of from 160 to 250° C., preferably 170 to227° C., more preferably from 175 to 224° C., and most preferably from180 to 220° C. When the melting point of the PVA resin is too high, themelting point and the degradation temperature become similar, as aresult of which the melt spinnability tends to decrease due to theoccurrence of decomposition during melt spinning.

Also, when the melting point of the PVA resin is too much lower than themelting point of the above-mentioned water-insoluble thermoplasticresin, this is undesirable because the melt spinnability decreases. Fromthis standpoint, the melting point of the PVA resin is preferably notmore than 60° C. lower, and more preferably not more than 30° C. lower,than the melting point of the water-insoluble thermoplastic resin.

The water-insoluble thermoplastic resin is preferably a thermoplasticresin which is not dissolved and removed, or decomposed and removed, bywater, an alkaline aqueous solution, an acid aqueous solution or thelike, and which is capable of being melt spun.

Illustrative examples of the water-insoluble thermoplastic resin includevarious types of the above-described thermoplastic resins that can beused to form the ultrafine fibers making up the polishing pad.

The water-insoluble thermoplastic resin may contain various additives.Examples of such additives include catalysts, discoloration inhibitors,heat stabilizers, flame inhibitors, lubricants, stain blockers,fluorescent whiteners, delusterants, colorants, gloss enhancers,antistatic agents, fragrances, deodorants, antimicrobial agents,miticides and inorganic fine particles.

Next, the method for melt spinning the above water-soluble thermoplasticresin and the above water-insoluble thermoplastic resin to form anislands-in-the-sea type composite fiber, and for forming a filament webfrom the resulting islands-in-the-sea type composite fibers, isdescribed in detail.

The filament web can be obtained by, for example, melt-spinning andthereby combining the water-soluble thermoplastic resin and thewater-insoluble thermoplastic resin, then by drawing and subsequentlydepositing the fibers using a spunbonding process. By forming a webusing a spunbonding process in this way, there can be obtained afilament web composed of islands-in-the-sea type composite fibers whichdoes not shed many fibers and has a high fiber density and good shapestability. As used herein, “filament” refers to a fiber which has beenmanufactured without passing through such a cutting step as a case inthe manufacture of a staple fiber.

In the manufacture of the islands-in-the-sea type composite fibers, thewater-soluble thermoplastic resin and the water-insoluble thermoplasticresin are separately melt-spun, and are combined. The mass ratio of thewater-soluble thermoplastic resin and the water-insoluble thermoplasticresin is in a range of preferably from 5/95 to 50/50, and morepreferably from 10/90 to 40/60. When the mass ratio of the water-solublethermoplastic resin and the water-insoluble thermoplastic resin is inthis range, an ultrafine fiber-entangled body having a high density canbe obtained, and the ultrafine fiber formability is also excellent.

After the water-soluble thermoplastic resin and the water-insolublethermoplastic resin have been combined by melt spinning, a filament webis formed by spunbonding as described below.

First, the water-soluble thermoplastic resin and the water-insolublethermoplastic resin are each melt-mixed in separate extruders, andstrands of the molten resins are simultaneously discharged from therespective differing spinnerets. Next, the discharged strands arecombined in a combining nozzle, then discharged from the nozzle orificesin the spinning head to form an islands-in-the-sea type composite fiber.To obtain fiber bundles having low individual fiber fineness and a highfiber density, it is desirable for the number of islands in theislands-in-the-sea type composite fiber during molten composite spinningto be preferably from 4 to 4,000 islands/fiber, and more preferably from10 to 1,000 islands/fiber.

The above islands-in-the-sea type composite fiber is cooled in a coolingdevice, following which a suction apparatus such as an air jet nozzle isused to draw the fiber with a high-speed stream of air at a velocityequivalent to the take-up speed of 1,000 to 6.000 m/min in such a way asto achieve the target fineness. Next, the drawn composite fibers aredeposited onto a movable collecting surface, thereby forming a filamentweb. At this time, if necessary, the deposited filament web may besubjected to localized pressure bonding. A basis weight for the fiberweb in a range of from 20 to 500 g/m² enables a uniform ultrafinefiber-entangled body to be obtained, and is also desirable from anindustrial standpoint.

(2) Web Entangling Step

Next, the web entangling step in which a sheet of entangled webs isformed by stacking and entangling a plurality of the above filament websis described.

An entangled web sheet is formed by using a known nonwoven fabricmanufacturing process such as needlepunching or hydroentanglement tocarry out an entangling treatment on the filament webs. By way ofillustration, a description is given below of the entangling treatmentby needlepunching.

First, a silicone finish or a mineral oil finish, such as a needle breakpreventing finish, an antistatic finish or an entanglement enhancingfinish, is applied to the filament web. To reduce variations in thebasis weight, the finish may be applied after superimposing two or morefiber webs in a crosslapped manner.

Next, the entangling treatment is carried out in which the fibers arethree-dimensionally entangled by needlepunching. By carrying out theneedlepunching treatment, an entangled web sheet which has a high fiberdensity and does not readily shed fibers can be obtained. The basisweight of the entangled web sheet is suitably selected in accordancewith the thickness and other properties of the target polishing pad. Forexample, a basis weight in a range of 100 to 1500 g/m² is desirable fromthe standpoint of excellent handleability.

The type and amount of the finish, and the needle conditions (e.g.,needle shape, needle depth, punch density) in needlepunching aresuitably selected in such a way as to give the entangled web sheet ahigh delamination strength between the layers of the sheet. The highernumber of barbs is preferable within a range where needle breakage doesnot arise. By way of illustration, the number of barbs may be selectedfrom among 1 to 9 barbs. The needle depth is preferably set in such away that the barbs penetrate to the surface of the stacked webs andwithin a range where the pattern after needlepunching does not emergestrongly on the web surface. Also, the needle punch density is adjustedaccording to such factors as the shape of the needles and the type andamount of the finish used, although a density of from 500 to 5,000punches/cm² is preferred. Carrying out the entangling treatment in sucha way that the ratio of the basis weight following the entanglingtreatment to the basis weight before the entangling treatment is 1.2 ormore, and especially 1.5 or more, is preferable from the standpoint ofobtaining an ultrafine fiber-entangled body having a high fiber densityand reducing the shedding of fibers. The upper limit is not subject toany particular limitation, although the ratio of 4 or less is preferableto avoid increased production costs due to a decrease in throughput.

If the polishing pad is to be used for polishing bare silicon wafers, itis preferable to set the void volume of the polishing pad to at least50%. For this reason, the amount of polymeric elastomer filled into thepolishing pad may be adjusted depending on whether the fiber density isto be increased or decreased.

A delamination strength for the entangled web sheet of at least 2 kg/2.5cm, and especially at least 4 kg/2.5 cm, is desirable for obtaining anultrafine fiber-entangled body which has a good shape retention, shedsfew fibers, and has a high fiber density. The delamination strengthserves as an indicator of the degree of three-dimensional entangling. Incases where the delamination strength is too low, the ultrafinefiber-entangled body will not have a sufficiently high fiber density.The upper limit in the delamination strength of the entangled nonwovenfabric is not subject to any particular limitation; however, from thestandpoint of the entangling treatment efficiency, it is preferably notmore than 30 kg/2.5 cm.

For the purpose of adjusting the hardness of the polishing pad, it ispossible, insofar as the advantageous effects of the invention areattainable, to use as the sheet of entangled webs a laminated structuresuch as an entangled nonwoven fabric that has been entangled and therebyunited with a knit or woven fabric (e.g., knit or woven fabric/entanglednonwoven fabric, entangled nonwoven fabric/knit or wovenfabric/entangled nonwoven fabric). Such a laminated structure isobtained by carrying out an entangling treatment wherein a knit or wovenfabric composed of ultrafine fibers is additionally superimposed on thesheet of entangled webs (a nonwoven fabric) obtained as described aboveand subjected to needlepunching and/or hydroentanglement.

The ultrafine fibers making up such a knit or woven fabric are notsubject to any particular limitation. Specifically, examples preferablyused include polyester fibers formed from polyethylene terephthalate(PET), polytrimethylene terephthalate, polybutylene terephthalate (PBT)or a polyester elastomer; polyamide fibers formed from polyamide 6,polyamide 66, aromatic polyamides or polyamide elastomers; and urethanepolymers, olefin polymers and acrylonitrile polymers. Of these, fibersformed of PET, PBT, polyamide 6, polyamide 66 or the like are preferredfrom an industrial standpoint.

Specific examples of the component removed from the islands-in-the-seatype composite fibers which form the above knit or woven fabric includepolystyrene and copolymers thereof, polyethylene, PVA resins,copolymeric polyester and copolymeric polyamide. Of these, the use of aPVA resin is preferred on account of the large shrinkage that arises atthe time of removal by dissolution.

(3) Wet Heat Shrinkage Treatment Step

Next, the wet heat shrinkage treatment step for increasing the fiberdensity and degree of entanglement in the sheet of entangled webs bysubjecting the sheet to wet heat shrinkage is described. In this step,subjecting the entangled web sheet containing filaments to wet heatshrinkage enables a considerable shrinkage compared with when anentangled web sheet containing staple fibers is subjected to wet heatshrinkage, thereby resulting in a particularly high fiber density forthe ultrafine fibers.

The wet heat shrinkage treatment is preferably carried out by steamheating. The steam heating conditions preferably entail a heat treatmentat an ambient temperature in a range of 60 to 130° C. and a relativehumidity of at least 75%, more preferably at least 90%, for a period of60 to 600 seconds. Such heating conditions are preferable because theentangled web sheet can be shrunk at a high shrinkage ratio. If therelative humidity is too low, water in contact with the fibers willrapidly dry, as a result of which shrinkage may be inadequate.

It is desirable for the wet heat shrinkage treatment to shrink theentangled web sheet by a surface area shrinkage ratio of at least 30%,preferably at least 35%, and more preferably at least 400/o. By inducingthe shrinkage at such a high shrinkage ratio, a high fiber density canbe achieved. The upper limit in the surface area shrinkage ratio is notsubject to any particular limitation. However, from the standpoint ofthe shrinkage limit and the treatment efficiency, a shrinkage ratio ofup to about 80% is preferred.

The surface area shrinkage ratio (%) is calculated from the followingformula (1):

[(surface area of sheet side before shrinkage treatment−surface area ofsheet side after shrinkage treatment)/surface area of sheet side beforeshrinkage treatment]×100  (1)

This surface area refers to the average surface area obtained from thesurface area of the front side of the sheet and the surface area of theback side of the sheet.

The ratio of the void volume of the entangled web sheet that has beensubjected to the wet heat shrinkage treatment in this way can beadjusted by hot rolling or hot pressing the sheet at or above the heatdistortion temperature of the islands-in-the-sea type composite fiber.By making the hot pressing conditions stronger, it is possible toincrease the fiber density and achieve greater compactness.

It is desirable for the change in the basis weight of the entangled websheet before and after the wet heat shrinkage treatment to be such thatthe basis weight following shrinkage treatment, as compared with thebasis weight before shrinkage treatment, is at least 1.2 times (massratio), and more preferably at least 1.5 times, but not more than 4times, and more preferably not more than 3 times.

(4) Fiber Bundle-Binding Step

Prior to carrying out an ultrafine fiber-forming treatment on theentangled web sheet, for the purpose of increasing the shape stabilityof the entangled web sheet, or for the purpose of adjusting or reducingthe void volume of the resulting polishing pad, if necessary, the fiberbundles may be bonded beforehand by impregnating the shrinkage-treatedentangled web sheet with an aqueous liquid of the polymeric elastomerand dry coagulating the elastomer.

In this step, the polymeric elastomer is filled into the entangled websheet by impregnating the shrinkage-treated entangled web sheet with anaqueous liquid of the polymeric elastomer and dry coagulating theelastomer. Because the aqueous liquid of the polymeric elastomer has alow viscosity even at high concentrations, and also has an excellentpenetrability during impregnation, a high degree of filling at theinterior of the entangled web sheet is easily achieved. It also has anexcellent adherence to the fibers. Therefore, by carrying out this step,it is possible to tightly restrain the islands-in-the-sea type compositefibers.

As used herein, “aqueous liquid of elastomeric polymer” refers to anaqueous solution obtained by dissolving the polymeric elastomer-formingingredients in an aqueous solvent, or an aqueous dispersion obtained bydispersing the polymeric elastomer-forming ingredients in an aqueousmedium. Here, “aqueous dispersion” includes suspension type dispersionsand emulsion type dispersions. The use of the aqueous dispersion isespecially preferred on account of the excellent water resistance.

The method of preparing the polyurethane resin as the aqueous solutionor the aqueous dispersion is not subject to any particular limitation.Use may be made of a known method, such as a method wherein thepolyurethane resin is imparted with dispersibility in an aqueous mediumby including therein a monomer unit having a hydrophilic group such as acarboxylic group, a sulfonic acid group or a hydroxyl group, or a methodwherein a surfactant is added to the polyurethane resin so as toemulsify or suspend the resin. Because such aqueous polymeric elastomershave an excellent water-wettability, they have an excellent ability toretain the abrasive, both uniformly and in a large amount.

Illustrative examples of surfactants that may be used in suchemulsification or suspension include anionic surfactants such as sodiumlauryl sulfate, ammonium lauryl sulfate, sodium polyoxyethylene tridecylether acetate, sodium dodecylbenzene sulfonate, sodium alkyldiphenylether disulfonate and sodium dioctylsulfosuccinate; and nonionicsurfactants such as polyoxyethylene nonyl phenyl ether, polyoxyethyleneoctyl phenyl ether, polyoxyethylene lauryl ether, polyoxyethylenestearyl ether and polyoxyethylene-polyoxypropylene block copolymer.Moreover, a so-called reactive surfactant which has reactivity may alsobe used. It is also possible, by suitably selecting the cloud point ofthe surfactant, to impart thermosensitive gelling properties to thepolyurethane resin. However, when a large amount of surfactants is used,this sometimes has adverse effects on the polishing performance and thepolishing stability over time. Hence, it is preferable to keep theamount of surfactants used to the minimum required.

By setting the solids concentration of the aqueous liquid of thepolymeric elastomer to at least 10 mass %, and preferably at least 15mass %, the void volume ratio can be reduced.

Examples of methods for impregnating the aqueous liquid of the polymericelastomer into the entangled web sheet include methods involving the useof a knife coater, bar coater or roll coater, and dipping methods.

The polymeric elastomer may then be coagulated by drying the entangledweb sheet into which the aqueous liquid of the polymeric elastomer hasbeen impregnated. Examples of drying methods include methods whichinvolve a heat treatment in a drying device at 50 to 200° C., andmethods wherein infrared heating is followed by a heat treatment in adrying device.

In cases where the entangled web sheet is dried after the aqueous liquidof the polymeric elastomer has been impregnated into the entangled websheet, a uniform filled state sometimes cannot be achieved on account ofmigration of the aqueous liquid to the surface layer of the entangledweb sheet. In such cases, the migration can be suppressed by, forexample, adjusting the particle size of the polymeric elastomer in theaqueous liquid; adjusting the type and amount of ionic groups on thepolymeric elastomer, or adjusting the stability thereof by means of thepH or the like; or lowering the water dispersion stability at about 40to 100° C. through the concomitant use of a monovalent or divalentalkali metal salt or alkaline earth metal salt, a nonionic emulsifyingagent, an associative water-soluble thickening agent, an associativethermosensitive gelling agent such as a water-soluble silicone compound,a water-soluble polyurethane compound, or an organic or inorganicsubstance which changes the pH under the effect of heating. Ifnecessary, the migration may be induced so that the polymeric elastomeris preferentially distributed in the surface.

(5) Ultrafine Fiber-Forming Step

Next, the ultrafine fiber-forming step, which is a step in whichultrafine fibers are formed by dissolving the water-solublethermoplastic resin in hot water, is described.

This is a step in which ultrafine fibers are formed by removing thewater-soluble thermoplastic resin. At this time, voids are formed inareas where the water-soluble thermoplastic resin in the entangled websheet has been dissolved and extracted. The polymeric elastomer isfilled into these voids in the subsequent polymeric elastomer fillingstep, as a result of which the ultrafine fibers converge as bundles, andthe bundles of ultrafine fibers are restrained.

The ultrafine fiber-forming treatment is a treatment in which theentangled web sheet, or a composite of the entangled web sheet with thepolymeric elastomer, is subjected to hot-water heat treatment withwater, an alkaline aqueous solution, an acidic aqueous solution or thelike so as to dissolve and remove, or decompose and remove, thewater-soluble thermoplastic resin.

In a preferred example of the hot-water heat treatment conditions, afirst stage consisting of 5 to 300 seconds of immersion in 65 to 90° C.hot water is followed by a second stage consisting of 100 to 600 secondsof treatment in 85 to 100° C. hot water. Also, to increase thedissolution efficiency, if necessary, nipping treatment with rollers,high-pressure water jet treatment, ultrasonic treatment, showertreatment, agitation treatment, rubbing treatment or the like may becarried out.

In this step, when the water-soluble thermoplastic resin dissolves fromthe islands-in-the-sea type composite fibers to form the ultrafinefibers, the ultrafine fibers undergo considerable shrinkage. Because thefiber density rises through such shrinkage, the ultrafinefiber-entangled body having a high-density is obtained.

(6) Polymeric Elastomer Filling Step

Next, a step is described wherein, by filling the polymeric elastomerinto the interior of the ultrafine fiber bundles formed of the ultrafinefibers, the ultrafine fibers are made to converge as bundles, inaddition to which the individual ultrafine fiber bundles are restrainedand, moreover, the ultrafine fiber bundles are bound to each other.

In the ultrafine fiber-forming step (5), by subjecting theislands-in-the-sea type composite fibers to ultrafine fiber-formingtreatment, the water-soluble thermoplastic resin was removed, resultingin the formation of voids at the interior of the ultrafine fiberbundles. In the present step, by suitably filling such voids with thepolymeric elastomer, the ultrafine fibers are made to converge asbundles, in addition to which the individual ultrafine fiber bundles arerestrained and the ultrafine fiber bundles are bound to each other,which makes it possible to set the void volume ratio in the polishingpad to, for example, 50% or less. Also, by filling with the polymericelastomer to a sufficient degree, the void volume ratio is lowered,making it possible to give the polishing pad a dense structure.Moreover, when the ultrafine fibers are formed into ultrafine fiberbundles, the aqueous fluid of the polymeric elastomer readilyimpregnates therein by way of a capillary effect, further facilitatingthe convergence of the ultrafine fibers into bundles and the restraintof the ultrafine fiber bundles.

The aqueous liquids of the polymeric elastomer that may be used in thisstep are the same as the aqueous liquids of polymeric elastomers thatwere mentioned above in the fiber bundle-binding step (4).

A method similar to that used in the fiber bundle-binding step (4) maybe suitably used in the present step as the method of filling thepolymeric elastomer into the interior of the ultrafine fiber bundlesformed of ultrafine fibers. In addition, the void volume ratio may beadjusted to the desired value by suitably combining the fiberbundle-binding step (4) and the polymeric elastomer filling step (6). Inthis way, the polishing pad is formed.

Post-Treatment of Polishing Pad

If necessary, the polishing pad obtained may be subjected to apost-treatment, such as molding, flattening, napping, lamination,surface treatment and washing.

The molding and flattening are treatments wherein the polishing padobtained is hot-press molded to a given thickness, or is cut to a givenoutside shape by grinding. The polishing pad is preferably ground to athickness of about 0.5 to 3 mm.

The napping refers to a treatment in which a mechanical frictional forceor abrasive force is applied to the surface of the polishing pad bymeans of sandpaper, card clothing, a diamond dresser or the like so asto separate the ultrafine fibers that have been made to converge intobundles. By the napping, the fiber bundles existing in the polishing padsurface are fibrillated to form a large number of ultrafine fibers onthe surface.

The lamination refers to a treatment in which the stiffness is adjustedby superimposing and laminating the resulting polishing pad on a backingmaterial. For example, by laminating the polishing pad together with anelastomer sheet having a low hardness, the global planarity of thesurface being polished (the planarity of the overall substrate beingpolished) can be further increased. Adhesion during such lamination maybe melt adhesion or adhesion using a non-pressure-sensitive adhesive ora pressure-sensitive adhesive. Illustrative examples of such backingmaterials include sheet-like backing materials, such as elastic spongebodies obtained from polyurethane or the like; nonwoven fabricsimpregnated with polyurethane (such as the product available from NittaHaas Inc. under the trade name Suba 400); elastomeric resin filmscomposed of a rubber such as natural rubber, nitrile rubber,polybutadiene rubber or silicone rubber, or a thermoplastic elastomersuch as polyester thermoplastic elastomer, polyamide thermoplasticelastomer or fluorinated thermoplastic elastomer; foamed plastics; andknit fabrics or woven fabrics.

The surface treatment refers to a treatment in which grooves or holes inthe form of a grid, concentric circles or spirals are formed on thesurface of the polishing pad in order to adjust the ability to retainand the ability to discharge the abrasive slurry.

The cleaning refers to a treatment of cleaning away impurities such asparticles and metal ions which adhere to the resulting polishing pad byusing cold water or warm water, or to a cleaning treatment with anaqueous solution or solvent containing an additive which has a cleansingaction, such as a surfactant.

The polishing pad of the present embodiment is preferably used forpolishing silicon wafers, compound semiconductor wafers, semiconductorwafers, semiconductor devices, liquid crystal members, opticalcomponents, quartz, optical substrates, electronic circuit substrates,electronic circuit mask substrates, multilayer wiring substrates, harddisks, and microelectromechanical system (MEMS) substrates. Because thepolishing pad of the embodiment has the void volume ratio that has beenset to at least 50%, it is particularly effective for polishing baresilicon wafers.

Specific examples of semiconductor wafers and semiconductor devicesinclude dielectric films made of silicon, silicon oxide, siliconoxyfluoride and organic polymers; wiring metal films made of copper,aluminum or tungsten; and barrier metal films made of tantalum,titanium, tantalum nitride or titanium nitride.

In polishing, the polishing pad may be used in any polishing step, suchas primary polishing, secondary polishing (adjustment polishing), finishpolishing and mirror polishing. Portions to be polished may be thefront, rear or end surface of a substrate.

EXAMPLES

The invention is illustrated more concretely below with examples,although the invention is not limited in any way by the examples.

Example 1

Islands-in-the-sea type composite fibers were formed by discharging awater-soluble thermoplastic polyvinyl alcohol resin (abbreviated belowas “PVA resin”) and an isophthalic acid-modified polyethyleneterephthalate having a degree of modification of 6 mol % (having a waterabsorption ratio when saturated with water at 50° C. of 1 mass % and aglass transition temperature of 77° C.; abbreviated below as “modifiedPET”) in a mass ratio of 20:80 from a spinneret for melt spinningcomposite fibers. The spinneret produced composite fibers having 50islands/fiber, and the spinneret temperature was 260° C. The ejectorpressure was adjusted so as to give a spinning speed of 4,000 m/min, andfilaments having an average fineness of 2.0 dtex was collected on a net,thereby giving a spunbonded sheet (filament web) with a basis weight of40 g/m².

Twelve of the resulting spunbonded sheets were superimposed in acrosslapped arrangement to produce a stack of webs having a total basisweight of 480 g/m². A needle break-preventing oil agent was then sprayedonto the resulting stacked webs. Next, using 1-barb 42-gauge needles and6-barb 42-gauge needles, the stacked webs were entangled byneedlepunching at 1800 punches/cm², thereby giving a sheet of entangledwebs. The entangled web sheet thus obtained had a basis weight of 750g/m². The surface area shrinkage due to the needlepunching treatment was35%.

Next, the resulting entangled web sheet was steam-treated for 90 secondsat 70° C. and 90% RH. The surface area shrinkage at this time was 40%.The sheet was then dried in a 140° C. oven and subsequently hot pressedat 140° C. to give an entangled web sheet having a basis weight of 1,250g/m², an apparent density of 0.65 g/cm³ and a thickness of 1.9 mm. Theentangled web sheet had a thickness after hot pressing which was 0.80times as thick as the sheet prior to hot pressing.

Next, the hot-pressed entangled web sheet was impregnated with anaqueous dispersion of polyurethane elastomer A (solids concentration, 20mass %) as the first polyurethane elastomer. Polyurethane elastomer Awas a noncrystalline polycarbonate-based non-yellowing-type polyurethaneresin which was prepared by polymerizing 55 mass % of, as the softcomponent, a polyol component obtained by mixing a noncrystallinepolycarbonate polyol (a copolymeric polyol composed of3-methyl-1,5-pentylene carbonate and hexamethylene carbonate) and apolyalkylene glycol having 2 to 3 carbons in a molar ratio of 99.7:0.3and adding to the mixture 1.5 mass % of a carboxylic group-containingmonomer (2,2-bis(hydroxymethyl)propionic acid), with4,4′-dicyclohexylmethane diisocyanate, a short-chain polyamine and ashort-chain polyol as the hard components. The water absorption ratio ofpolyurethane elastomer A was 3 mass %, the storage modulus at 23° C. was300 MPa, the storage modulus at 50° C. was 150 MPa, the glass transitiontemperature was −20° C. and the average particle size of the aqueousdispersion was 0.03 μm. The amount of adherent solids of the aqueousdispersion at this time was 10 mass % with respect to the mass of theentangled web sheet. The entangled web sheet impregnated with theaqueous dispersion was subjected to dry coagulation treatment at 90° C.and 50% RH, then dried at 140° C. The dried sheet was then hot-pressedat 140° C., giving a sheet having a basis weight of 1,370 g/m², anapparent density of 0.76 g/cm³ and a thickness of 1.8 mm.

Next, the entangled web sheet filled with polyurethane elastomer A wastreated with nip rollers, then immersed for 10 minutes in 95° C. hotwater while being subjected to high-pressure water jet treatment so asto dissolve and remove the PVA resin. This was followed by drying,thereby giving a composite of polyurethane elastomer A with an ultrafinefiber-entangled body, in which the composite was composed of ultrafinefibers having an average fineness of 0.05 dtex, and had a basis weightof 1,220 g/m², an apparent density of 0.66 g/cm³ and a thickness of 1.85mm.

This composite was then impregnated with an aqueous dispersion ofpolyurethane elastomer B (solid concentration, 30 mass %) as the secondpolyurethane elastomer. Polyurethane elastomer B was a polyurethaneresin prepared by using 100 parts by mass of a polycarbonate-basednon-yellowing-type polyurethane resin, adding 5 parts by mass of acarbodiimide crosslinking agent, and heat treating so as to form acrosslinked structure, in which the polycarbonate-basednon-yellowing-type polyurethane resin was obtained by polymerizing 50mass % of the soft component obtained by mixing a noncrystallinepolycarbonate polyol (a copolymeric polyol composed of hexamethylenecarbonate and pentamethylene carbonate) and a polyalkylene glycol having2 to 3 carbons in a molar ratio of 99.9:0.1, and adding to the mixture1.5 mass % of a carboxylic group-containing monomer(2,2-bis(hydroxymethyl)propionic acid), with 4,4′-dicyclohexylmethanediisocyanate, a short-chain amine and a short-chain diol as the hardcomponents. The water absorption ratio for polyurethane elastomer B was2 mass %, the storage modulus at 23° C. was 450 MPa, the storage modulusat 50° C. was 300 MPa, the glass transition temperature was −25° C. andthe average particle size of the aqueous dispersion was 0.05 μm. Theamount of adherent solids of the aqueous dispersion at this time was 15mass % with respect to the mass of the composite. Next, the compositeimpregnated with the aqueous dispersion was subjected to coagulationtreatment at 90° C. and 50% RH, then to drying treatment at 140° C. Thedried composite was then hot-pressed at 140° C., giving a polishing padprecursor. The resulting polishing pad precursor had a basis weight of1,390 g/m², an apparent density of 0.80 g/cm³ and a thickness of 1.75mm.

In the polishing pad precursor thus obtained, all 50 fibers of theultrafine fibers making up each fiber bundle converged as a bundle.Moreover, the polymeric elastomer was present at the interior of theultrafine fiber bundles, and restrained the bundles.

The resulting polishing pad precursor was subjected to grindingtreatment to flatten the surface, thereby giving a flattened pad havinga basis weight of 1,120 g/m², an apparent density of 0.80 g/cm³ and athickness of 1.4 mm. In addition, the pad was cut into circular shapeshaving a diameter of 51 cm, following which grooves having a width of2.0 mm and a depth of 1.0 mm were formed in a grid at 15.0 mm intervalson the surface, thereby giving circular polishing pads. The mass ratioof the ultrafine fiber-entangled body to the polyurethane elastomer was76/24, and the ratio of polymeric elastomer A to polymeric elastomer Bwas 40/60. The resulting polishing pads were evaluated by thebelow-described methods. The results are shown in Table 1.

Example 2

The same procedure as in Example 1 was carried out up to the productionof the entangled web sheet. After being hot-pressed without beingimpregnated with polyurethane elastomer A, the entangled web sheet wasthen immersed for 10 minutes in 95° C. hot water and the PVA resin wasdissolved and removed, thereby giving an ultrafine fiber-entangled bodycomposed of bundles of ultrafine fibers. The resulting ultrafinefiber-entangled body was then impregnated with an aqueous dispersion ofpolyurethane elastomer B (solids concentration, 40 mass %). At thistime, the amount of adherent solids of the aqueous dispersion was 20mass % with respect to the mass of the ultrafine fiber-entangled body.Next, the ultrafine fiber-entangled body impregnated with the aqueousdispersion was coagulated at 90° C. and 50% RH. This was followed bydrying treatment at 140° C., then hot pressing at 140° C. thereby givinga polishing pad precursor. The resulting polishing pad precursor waspost-treated in the same way as in Example 1, giving a flattened padhaving a basis weight of 1,080 g/m², an apparent density of 0.77 g/cm³and a thickness of 1.4 mm. Following a treatment to form grooves,circular polishing pads were obtained. In the resulting polishing pads,all 50 fibers of the ultrafine fibers making up each fiber bundleconverged as a bundle. Moreover, the polymeric elastomer was present atthe interior of the ultrafine fiber bundles, and restrained the bundles.The resulting polishing pads were evaluated by the below-describedmethods. The results are shown in Table 1.

Example 3

Aside from not carrying out the hot pressing treatment before theimpregnation of polyurethane elastomer A and also not carrying the hotpressing treatment after impregnation and drying, polishing pads wereobtained in the same way as in Example 1.

The polishing pad precursor thus obtained had a basis weight of 1,360g/m², an apparent density of 0.62 g/cm³ and a thickness of 2.2 mm, inaddition to which the mass ratio of the ultrafine fiber-entangled bodyto the polyurethane elastomer was 70/30. In the resulting polishing padprecursor, all 50 fibers of the ultrafine fibers making up each fiberbundle converged as a bundle. Moreover, the polymeric elastomer waspresent at the interior of the ultrafine fiber bundles, and restrainedthe bundles. Polishing pads obtained by carrying out flattening andgroove-forming treatment in the same way as in Example 1 were evaluatedby the below-described methods. The results are shown in Table 1.

Example 4

Aside from the use as the first polyurethane elastomer of, instead ofpolyurethane elastomer A, a polycarbonate-based non-yellowing-typepolyurethane elastomer C (water absorption ratio, 4%; storage modulus at23° C., 250 MPa; storage modulus at 50° C., 100 MPa; glass transitiontemperature, −30° C.; average particle size of aqueous dispersion, 0.03μm) obtained by polymerizing 58 mass % of, as the soft component, apolyol component composed of a polyether-based polyalkylene glycol mixedwith a polycarbonate polyol in a molar ratio of 88:12 and additionallycontaining 1.2 mass % of a carboxylic group-containing monomer(2,2-bis(hydroxymethyl)propionic acid), with isophorone diisocyanate, ashort-chain polyamine and a short-chain polyol as the hard components;and aside from the use as the second polyurethane elastomer of, insteadof polyurethane elastomer B, a polyurethane elastomer D (waterabsorption ratio, 4%; storage modulus at 23° C., 300 MPa, storagemodulus at 50° C., 125 MPa; glass transition temperature, −30° C.;average particle size of aqueous dispersion, 0.05 μm) obtained byincreasing the polyol component of polyurethane elastomer B by 10 mass %to set the amount of the polyol component relative to the polyurethaneelastomer at 60 mass %, polishing pads were produced in the same way asin Example 1. In the resulting polishing pads, all 50 fibers of theultrafine fibers making up each fiber bundle converged as a bundle.Moreover, the polymeric elastomer was present at the interior of theultrafine fiber bundles, and restrained the bundles. The resultingpolishing pads were evaluated by the below-described methods. Theresults are shown in Table 1.

Example 5

Aside from carrying out melt spinning by discharging a PVA resin and amodified PET in a mass ratio of 20:80 from a spinneret having 9islands/fiber, polishing pads were obtained in the same way as inExample 1. The average fineness of the ultrafine fibers was 0.28 dtex.In the resulting polishing pads, all 9 fibers of the ultrafine fibersmaking up each bundle converged as a bundle. Moreover, the polymericelastomer was present at the interior of the ultrafine fiber bundles,and restrained the bundles. The resulting polishing pads were evaluatedby the below-described methods. The results are shown in Table 1.

Example 6

Aside from changing as follows the polishing conditions in thebelow-described polishing pad evaluations, the polishing performance wasevaluated in the same way using the polishing pads obtained inExample 1. The polishing conditions were as follows.

(1) Aside from changing the silicon wafer having an oxide film to a baresilicon wafer and changing the slurry used in polishing to Glanzox 1103,available from Fujimi Incorporated, evaluation was carried out in thesame way.

(2) Aside from changing the slurry used in polishing to the polishingslurry GPL-C1010, available from Showa Denko KK, and changing the slurryflow rate to 200 mL, evaluation was carried out in the same way.

(3) Aside from changing the wafer to a tungsten wafer and changing theslurry used in polishing to W-2000, available from Cabot Corporation (34g of hydrogen peroxide added per 1,030 g of slurry), evaluation wascarried out in the same way.

(4) Aside from changing the wafer to a GaAs wafer, changing the slurryused in polishing to INSEC-FP, available from Fujimi Incorporated, andchanging the polishing pressure to 20 kPa, evaluation was carried out inthe same way.

The results are shown in Table 3.

Example 7

The same procedure as in Example 1 was carried out up to theimpregnation of polyurethane elastomer A to the interior of ahot-pressed entangled web sheet (basis weight, 1,280 g/m²; apparentdensity, 0.56 g/cm³; thickness, 2.3 mm) and the subsequentdry-coagulation. A sheet having a basis weight of 1,340 g/m², anapparent density of 0.69 g/cm³ and a thickness of 1.95 mm was obtainedwithout carrying out hot pressing.

Next, the entangled web sheet filled with polyurethane elastomer A wastreated with nip rollers, then immersed in 95° C. hot water for 10minutes while being high-pressure-water jet treated so as to dissolveand remove the PVA resin, and subsequently dried, thereby giving acomposite of polyurethane elastomer A and an ultrafine fiber-entangledbody in which the composite had the average fineness of the ultrafinefibers of 0.05 dtex, a basis weight of 1.050 g/m², an apparent densityof 0.57 g/cm³ and a thickness of 1.85 mm.

This composite was then impregnated with polyurethane elastomer B as thesecond polyurethane elastomer, following which the elastomer wasdry-coagulated, and hot pressing was not carried out, thereby giving apolishing pad precursor. The polishing pad precursor had a basis weightof 1,170 g/m², an apparent density of 0.60 g/cm³ and a thickness of 1.95mm.

The polishing pad precursor was then subjected to grinding treatment forsurface flattening, thereby giving a flattened pad having a basis weightof 1,000 g/m², an apparent density of 0.57 g/cm³ and a thickness of 1.75mm. This pad was cut into circular shapes having a diameter of 51 cm,and grooves with a width of 2.0 mm and a depth of 1.0 mm were formed ina grid on the surface at intervals of 15.0 mm, thereby giving circularpolishing pads. The mass ratio of the ultrafine fiber-entangled body tothe polyurethane elastomer was 76/24, and the ratio of polymericelastomer A to polymeric elastomer B was 40/60. The resulting polishingpads were evaluated by the below-described methods. The results areshown in Table 1.

Example 8

Aside from changing in the same way in (1) to (3) of Example 6 thepolishing conditions in the below-described polishing pad evaluations,the polishing performance was evaluated in the same way using thepolishing pads obtained in Example 7.

The results are shown in Table 4.

Comparative Example 1

Ny filaments having an average fineness of 2 dtex were melt-spun bymelt-spinning Ny 6. The resulting filaments were collected on a net,thereby giving a spunbonded sheet (filament web) having a basis weightof 30 g/m².

Stacked webs were formed in the same way as in Example 2 from theresulting spunbonded sheet. Next, the resulting stacked webs wereentangled by needlepunching in the same way as in Example 1, therebygiving an entangled web sheet. The resulting entangled web sheet had abasis weight of 800 g/m². Hot pressing at 140° C. was then carried out,thereby giving an entangled web sheet having an apparent density of 0.42g/cm³ and a thickness of 1.9 mm.

Next, an aqueous dispersion of polyurethane elastomer B (solidsconcentration, 30 mass %) was impregnated into the hot-pressed entangledweb sheet. The amount of adherent solids of the aqueous dispersion atthis time was 20 mass % with respect to the mass of the entangled websheet. The entangled web sheet impregnated with the aqueous dispersionwas then subjected to coagulation treatment at 90° C. and 90% RH, andalso subjected to drying treatment at 140° C., after which hot pressingtreatment was carried out at 140° C., thereby giving a polishing padprecursor having a basis weight of 920 g/m², an apparent density of 0.54g/m² and a thickness of 1.7 mm. Buffing treatment was then carried outto flatten the front and back faces, thereby giving a polishing pad. Theresulting polishing pad was evaluated by the below-described methods.The results are shown in Table 2.

Comparative Example 2

Instead of using an aqueous dispersion of polyurethane elastomer A toform a polyurethane elastomer, an aqueous dispersion of polyurethaneelastomer E (solids concentration, 20 mass %) was impregnated as thepolymeric elastomer. Polyurethane elastomer E was a non-yellowing-typepolyurethane resin obtained by polymerizing a polyol (60 mass % relativeto the polyurethane elastomer) composed of polyethylene glycol andpolytetramethylene glycol in a 15/85 mixture with isophoronediisocyanate, a short-chain polyamine and a short-chain polyol as thehard components. Polyurethane elastomer E had a water absorption ratioof 12 mass %, a storage modulus at 23° C. of 200 MPa, a storage modulusat 50° C. of 80 MPa, a glass transition temperature of −48° C., and anaverage particle size in the aqueous dispersion of 0.4 μm. Aside fromthis, polishing pads were produced in the same way as in Example 2. Theresulting polishing pads were evaluated by the below-described methods.The results are shown in Table 2.

Comparative Example 3

Aside from using polyurethane elastomer F (water absorption ratio, 8%;storage modulus at 23° C., 80 MPa, storage modulus at 50° C., 30 MPa;glass transition temperature, −32° C.; average particle size of aqueousdispersion, 0.02 μm) obtained by increasing the polyol component ofpolyurethane elastomer B to 65 mass %, polishing pads were produced inthe same way as in Example 2. The resulting polishing pads wereevaluated by the below-described methods. The results are shown in Table2.

Comparative Example 4

Aside from the use of polyurethane elastomer G (water absorption ratio,1%; storage modulus at 23° C., 1,000 MPa, storage modulus at 50° C., 200MPa; glass transition temperature, 0° C.; average particle size ofaqueous dispersion, 0.08 m) obtained by changing the polyol component ofpolyurethane elastomer B to hexamethylene carbonate diol, using 30 mass% of the soft (polyol) component and polymerizing this with4,4′-dicyclohexylmethane diisocyanate, a short-chain amine and ashort-chain diol as the hard components, polishing pads were produced inthe same way as in Example 2. The resulting polishing pads wereevaluated by the below-described methods. The results are shown in Table2.

The polishing pads obtained were evaluated by the following methods.

Evaluation Methods

(1) Average Fineness of Ultrafine Fibers, and Verification of ConvergingState of Ultrafine Fibers of Fiber Bundles

The polishing pad obtained was cut in the thickness direction with acutter blade, thereby forming a cut face in the thickness direction. Thecut face was dyed with osmium oxide, then examined at a magnification of500 to 1,000× with a scanning electron microscope (SEM), and the imagewas photographed. The cross-sectional area of the ultrafine fiberspresent in the cut face was then determined from the resulting image.This was calculated from the average cross-sectional surface areaobtained by averaging the cross-sectional areas at 100 randomly selectedplaces and from the density of the resin making up the fibers. Inaddition, the image obtained was observed. When not only ultrafinefibers making up the outside edge of the fiber bundle but also ultrafinefibers at the interior were bonded and integrally united to each otherby the polymeric elastomer, the ultrafine fibers were judged to be“converging”. When little or no polymeric elastomer was present at theinterior of the fiber bundles and the ultrafine fibers were in asubstantially unbonded and un-united state, the ultrafine fibers werejudged to be “non-converging”.

(2) Storage Moduli of Polymeric Elastomer at 23° C. and 50° C.

The polymeric elastomer used in the polishing pad was prepared as filmsamples having a length of 4 cm, a width of 0.5 cm and a thickness of400 μm±100 μm. Next, the sample thickness was measured with amicrometer, following which a dynamic viscoelastic analyzer (DVERheospectra, manufactured by Rheology Co., Ltd.) was used to measure thedynamic viscoelastic moduli at 23° C. and 50° C. under the followingconditions: frequency, 11 Hz; temperature ramp-up rate, 3° C./min. Thestorage moduli were computed from the measured results. In cases wheretwo types of polymeric elastomer were used, samples of each wereprepared and measured, and the sum of the values obtained by multiplyingby the respective mass ratio was used as the storage modulus for thepolymeric elastomers.

(3) Glass Transition Temperature of Polymeric Elastomer

The polymeric elastomer used in the polishing pad was prepared as a filmhaving a length of 4 cm, a width of 0.5 cm and a thickness of 400 μm±100μm. The sample thickness was measured with a micrometer, following whichthe dynamic viscoelasticity was measured at a frequency of 11 Hz and atemperature ramp-up rate of 3° C./min using a dynamic viscoelasticanalyzer (DVE Rheospectra, manufactured by Rheology Co., Ltd.), and themain dispersion peak temperature of the loss modulus was treated as theglass transition temperature. In cases where two types of polymericelastomer were used, samples of each were prepared and measured, and thesum of the values obtained by multiplying by the respective weight ratiowas used as the storage modulus for the polymeric elastomers.

(4) Water Absorption Ratio of Polymeric Elastomer upon Saturation withWater at 50° C.

A 200 μm thick film obtained by drying the polymeric elastomer at 50° C.was heat-treated at 130° C. for 30 minutes, then held for 3 days at 20°C. and 65% RH to form a dry sample which was immersed in 50° C. waterfor two days. The sample was then removed from the 50° C. water,immediately after which excess water droplets, etc. on the topmostsurface of the film were wiped off with a JK Wiper 150-S(Nippon PaperCrecia Co., Ltd.), thereby giving a water-swollen sample. The weights ofthe dry sample and the water-swollen sample were measured, and the waterabsorption ratio was determined according to the following formula.

Water absorption ratio (mass %)=[(mass of water-swollen sample−mass ofdry sample)/(mass of dry sample)]×100

In cases where two types of polymeric elastomer were used, samples ofeach were prepared and measured, and the sum of the values obtained bymultiplying by the respective weight ratio was used as the storagemodulus for the polymeric elastomers.

(5) Water Absorption Ratio of Ultrafine Fibers upon Saturation withWater at 50° C. (water absorption ratio of thermoplastic resin making upultrafine fibers upon saturation with water at 50° C.)

A 200 m thick film obtained by hot-pressing the thermoplastic resinmaking up the ultrafine fibers at a temperature of the melting point+20to 100° C. was heat-treated at 130° C. for 30 minutes, then held for 3days at 20° C. and 65% RH to form a dry sample, which was subsequentlyimmersed in 50° C. water for two days. The sample was then removed fromthe water, immediately after which excess water droplets, etc. on thetopmost surface of the film were wiped off with a JK Wiper 150-S(NipponPaper Crecia Co., Ltd.), thereby giving a water-swollen sample. Theweights of the dry sample and the water-swollen sample were measured,and the water absorption ratio was determined according to the followingformula.

Water absorption ratio (mass %)=[(mass of water-swollen sample−mass ofdry sample)/(mass of dry sample)]×100

(6) Average Particle Size of Aqueous Polyurethane

The average particle size of the water-dispersed polymeric elastomer wasdetermined through measurement by dynamic light scattering using aELS-800 system (Otsuka Chemical Co., Ltd.) and analysis by the cumulantmethod (described in Koroido kagaku [Colloidal chemistry] Vol. IV:Koroido kagaku jikken-hō [Experimental methods in colloidal chemistry],published by Tokyo Kagaku Dojin). In cases where two types of polymericelastomer were used, samples of each were measured, and the sum of thevalues obtained by multiplying by the respective weight ratio was usedas the storage modulus for the polymeric elastomers.

(7) Apparent Density of Polishing Pad and Void Volume Ratio of PolishingPad (Volumetric Ratio of Void Areas in Polishing Pad)

The apparent density of the polishing pad was measured in generalaccordance with JIS L1096. At the same time, the theoretical density ofthe composite of the ultrafine fiber-entangled body with the polymericelastomer in the absence of voids was calculated from the compositionalratios of the respective components in the polishing pad and thedensities of each of these components. In addition, the ratio of theapparent density to the theoretical density was treated as thevolumetric ratio of the filled areas in the polishing pad, and [1−(ratioof apparent density to theoretical density)]×100(%) was treated as thevoid volume ratio of the polishing pad (volumetric ratio of void areasin the polishing pad). The densities of the components used in Example 1were as follows: modified PET, 1.38 g/cm³; polyurethane elastomer, 1.05g/cm³; PVA resin, 1.25 g/cm³.

(8) Evaluation of Polishing Performance by Polishing Pad

A pressure-sensitive adhesive tape was bonded to the back side of acircular polishing pad, following which the pad was mounted on a CMPpolisher (PP0-60S, manufactured by Nomura Machine Tool Works. Ltd.).Next, using a 200-grit diamond dresser (MEC 200L, available fromMitsubishi Materials Corporation), conditioning (seasoning) was carriedout by grinding the surface of the polishing pad for 18 minutes at apressure of 177 kPa and a dresser rotational speed of 110 rpm under aflow of distilled water at a rate of 120 mL/min.

Next, a 6-inch diameter silicon wafer having an oxide film surface waspolished for 100 seconds at a platen speed of 50 rpm, a head speed of 49rpm and a polishing pressure of 35 kPa while supplying an abrasiveslurry (SS 12, available from Cabot Corporation) at a rate of 120mL/min. The thickness after polishing at 49 randomly selected points inthe plane of the silicon wafer having an oxide film surface wasmeasured, and the polishing rate (nm/min) was determined by dividing thepolished thickness at each point by the polishing time. In addition, thepolishing rate (R) was calculated as the average value of the polishingrates at the 49 points, and the standard deviation (σ) was determined.

The planarity was then evaluated from the following formula. A smallerplanarity value indicates a better planarization performance.

Planarity (%)=(σ/R)×100

Next, the polishing pad used in the above polishing operation was heldin a wet state at 25° C. for 24 hours, then the polishing pad wasseasoned and used again to carry out polishing, following which thepolishing rate (R) and planarity were determined.

Seasoning and polishing were alternately repeated in this way 300 times,and the polishing rate (R) and planarity after 300 polishing cycles weredetermined.

The number of scratches at least 0.16 μm in size present on the surfaceof the silicon wafer having an oxide film after each polishing operationwas determined using a wafer surface inspection system (Surfscan SPI,available from KLA-Tencor), based on which the tendency for scratchingto occur was evaluated.

(9) Evaluation of Polishing Performance by Polishing Pad in Bare SiliconWafer Polishing

A pressure-sensitive adhesive tape was bonded to the back side of acircular polishing pad, following which the pad was mounted on a CMPpolisher (PP0-60S, manufactured by Nomura Machine Tool Works. Ltd.).Next, using a 200-grit diamond dresser (MEC 200L, available fromMitsubishi Materials Corporation), conditioning (seasoning) was carriedout by grinding the surface of the polishing pad for 18 minutes at apressure of 177 kPa and a dresser rotational speed of 110 rpm under aflow of distilled water at a rate of 120 mL/min.

Next, a 6-inch diameter silicon wafer was polished for 100 seconds at aplaten speed of 50 rpm, a head speed of 49 rpm and a polishing pressureof 35 kPa while supplying Glanzox 1103 (Fujimi Incorporated) at a rateof 120 mL/min. The thickness after polishing at 49 randomly selectedpoints in the plane of the silicon wafer was measured, and the polishingrate (nm/min) was determined by dividing the polished thickness at eachpoint by the polishing time. In addition, the polishing rate (R) wascalculated as the average value of the polishing rates at the 49 points,and the standard deviation (σ) was determined.

The planarity was then evaluated from the following formula. A smallerplanarity value indicates a better planarization performance.

Planarity (%)=(σ/R)×100

Next, the polishing pad used in the above polishing operation was heldin a wet state at 25° C. for 24 hours, then the polishing pad wasseasoned and used again to carry out polishing, following which thepolishing rate (R) and planarity were determined.

Seasoning and polishing were alternately repeated in this way 300 times,and the polishing rate (R) and planarity after 300 polishing cycles weredetermined.

The results for Examples 1 to 5 and 7 are shown in Table 1, the resultsfor Example 6 are shown in Table 3, the results for Example 8 are shownin Table 4, and the results for Comparative Examples 1 to 4 are shown inTable 2.

TABLE 1 Example No. 1 2 3 4 5 7 Average fineness of ultrafine fibersdtex 0.05 0.05 0.05 0.05 0.05 0.05 Number of ultrafine fibers of fibernumber 50 50 50 50 9 50 bundles Converging state of ultrafine fibers —converging converging converging converging converging converging offiber bundles Type of thermoplastic resin in isophthalate- isophthalate-isophthalate- isophthalate- isophthalate- isophthalate- ultrafine fibersmodified modified modified modified modified modified polyethylenepolyethylene polyethylene polyethylene polyethylene polyethyleneterephthalate terephthalate terephthalate terephthalate terephthalateterephthalate Glass transition temperature of ° C. −23 −25 −23 −30 −23−23 polymeric elastomer Water absorption ratio of polymeric mass % 2.4 22.4 4 2.4 2.4 elastomer upon saturation (50° C.) Storage modulus ofpolymeric MPa 390 450 390 280 390 390 elastomer at 23° C. Storagemodulus of polymeric MPa 240 300 240 115 240 240 elastomer at 50° C.Ratio of storage moduli at 23° C. — 1.6 1.5 1.6 2.4 1.6 1.6 and 50° C.of polymeric elastomer Polycarbonate ratio in polyol % >99 >99 >9995 >99 >99 component of polymeric elastomer Average particle size ofaqueous μm 0.04 0.05 0.04 0.04 0.04 0.04 polyurethane Ultrafinefiber-entangled body/polymeric 76/24 83/17 70/30 76/24 76/24 76/24elastomer (mass ratio) Apparent density of polishing pad g/cm³ 0.8 0.770.62 0.8 0.8 0.57 Void volume ratio of polishing pad vol % 38 42 52 3838 56 Polishing rate (initial) nm/min 190 200 210 200 210 210 (after 24hours) 200 200 220 210 220 220 (after 300 polishing cycles) 200 200 210200 220 210 Planarity (initial) % 6 6 7 6 7 7 (after 24 hours) 5 5 6 6 76 (after 300 polishing cycles) 5 6 6 7 6 7 Scratches (initial) number 1210 8 10 15 10 (after 24 hours) number 10 10 10 10 12 10 (after 300cycles) number 8 11 10 14 12 8

TABLE 2 Comparative Examples 1 to 4 1 2 3 4 Average fineness ofultrafine fibers dtex 1 0.05 0.05 0.05 Number of ultrafine fibers offiber bundles number 1 50 50 50 Converging state of ultrafine fibers of— — converging converging converging fiber bundles Type of thermoplasticresin in ultrafine fibers Ny6 isophthalate-modified isophthlate-modifiedisophthalate-modified polyethylene polyethylene polyethyleneterephthalate terephthalate terephthalate Glass transition temperatureof polymeric ° C. −25 −48 −32 0 elastomer Water absorption ratio ofpolymeric elastomer mass % 2 12 8 1 upon saturation (50° C.) Storagemodulus of polymeric elastomer at 23° C. MPa 450 200 80 1000 Storagemodulus of polymeric elastomer at 50° C. MPa 300 80 30 200 Ratio ofstorage moduli at 23° C. and — 1.5 2.5 2.7 5 50° C. of polymericelastomer Polycarbonate ratio in polyol component % >99 0 >99 >90 ofpolymeric elastomer Average particle size of aqueous polyurethane μm0.05 0.4 0.02 0.08 Ultrafine fiber-entangled body/polymeric 83/17 83/1776/24 76/24 elastomer (mass ratio) Apparent density of polishing padg/cm³ 0.54 0.8 0.8 0.8 Void volume ratio of polishing pad vol % 52 40 3838 Polishing rate (initial) 160 200 210 210 (after 24 hours) nm/min 160180 220 230 (after 300 polishing cycles) 170 150 220 230 Planarity(initial) % 8 8 14 6 (after 24 hours) 9 10 16 6 (after 300 polishingcycles) 10 15 20 1.0 Scratches (initial) number 15 8 10 50 (after 24hours) number 40 20 18 80 (after 300 cycles) number 60 40 25 140

TABLE 3 Type of polishing pad Polishing pad of Example 1 PolishingConditions (1) (2) (3) (4) Polishing rate (initial) nm/min 580 540 150780 (after 24 hours) 620 560 140 800 (after 300 polishing cycles) 630560 140 780 Planarity (initial) % 7 7 7 8 (after 24 hours) 7 8 7 9(after 300 polishing cycles) 8 8 8 9 Scratches (initial) number — 15 — —(after 24 hours) number — 12 — — (after 300 polishing cycles) number —12 — —

TABLE 4 Polishing pad Type of polishing pad of Example 7 PolishingConditions (1) (2) (3) Polishing rate (initial) nm/min 720 620 140(after 24 hours) 756 630 150 (after 300 polishing cycles) 760 610 160Planarity (initial) % 6 7 7 (after 24 hours) 7 6 8 (after 300 polishingcycles) 6 7 9

As explained above, one aspect of the invention relates to a polishingpad which comprises an ultrafine fiber-entangled body formed ofultrafine fibers having an average fineness of 0.01 to 0.8 dtex, and apolymeric elastomer, wherein the polymeric elastomer has a glasstransition temperature of −10° C. or below, storage moduli at 23° C. and50° C. of 90 to 900 MPa, and a water absorption ratio, when saturatedwith water at 50° C., of 0.2 to 5 mass %.

According to this arrangement, there can be obtained a polishing padwhich is capable of carrying out, with long-term stability, polishingthat achieves a high planarity while suppressing the occurrence ofscratches.

It is preferable for the ultrafine fiber-entangled body to be composedof bundles of 5 to 70 ultrafine fibers, and for the polymeric elastomerto be present inside the ultrafine fiber bundles.

According to this arrangement, the polymeric elastomer makes theultrafine fibers converge as bundles and also restrains the ultrafinefiber bundles, thereby increasing the stiffness of the polishing pad andenabling the planarization performance, polishing uniformity andstability over time to be enhanced.

It is preferable for the ultrafine fibers be formed of polyester fibersbecause this enables the ultrafine fiber-entangled body that is compactand has a high density to be formed.

It is preferable for the ultrafine fibers to be formed of athermoplastic resin having a water absorption ratio, when saturated withwater at 50° C., of 0.2 to 2 mass %.

This arrangement enables the polishing pad to be obtained whichsuppresses the decrease over time in the planarization performance andundergoes little fluctuation in polishing rate and polishing uniformity.

It is preferable that the polymeric elastomer is a polyurethane resinobtained by using a polyol, a polyamine and a polyisocyanate, and that60 to 100 mass % of the polyol is a noncrystalline polycarbonate diol.

According to this arrangement, the resistance to the slurry used inpolishing is high, enabling a good stability over time to be maintainedduring polishing.

It is preferable for the polymeric elastomer to be a polyurethane resinobtained by using as the polyol a noncrystalline polycarbonate dioltogether with a carboxylic group-containing diol, and by using analicyclic diisocyanate as the polyisocyanate.

According to this arrangement, the polymeric elastomer can easily beadjusted to the glass transition temperature of −10° C. or less, thestorage moduli at 23° C. and 50° C. of 90 to 900 MPa, and the waterabsorption ratio, when saturated with water at 50° C. of 0.2 to 5mass/0%.

It is preferable that the polymeric elastomer has a ratio of the storagemodulus at 23° C. to the storage modulus at 50° C. (storage modulus at23° C./storage modulus at 50° C.) being 4 or less.

According to this arrangement, even when a temperature change occursduring polishing, the storage moduli do not readily change, as a resultof which the stability over time during polishing can be enhanced.

It is preferable for the polymeric elastomer to be an aqueouspolyurethane having an average particle size of 0.01 to 0.2 μm because agood water resistance is achieved and the fiber bundle restraining forceincreases.

It is preferable for the mass ratio of the ultrafine fiber-entangledbody and the polymeric elastomer (ultrafine fiber-entangledbody/polymeric elastomer) to be from 55/45 to 95/5 because the polishingefficiency is enhanced and the pad wear during polishing decreases.

It is preferable for void areas in the polishing pad to have a volumeratio of at least 50%.

According to this arrangement, because the polishing pad has both goodslurry retention and suitable stiffness and cushionability it can beadvantageously used for polishing bare silicon wafers.

Another aspect of the invention relates to a method for manufacturing apolishing pad, the method comprising a step of filling the interior ofbundles of ultrafine fibers which have an average fineness of from 0.01to 0.8 dtex with a polymeric elastomer having a glass transitiontemperature of −10° C. or below, storage moduli at 23° C. and 50° C. of90 to 900 MPa. and a water absorption ratio, when saturated with waterat 50° C., of 0.2 to 5 mass %.

According to this arrangement, the polishing pad which has a highstiffness and high abrasive slurry retention and which do not readilyform scratches on the substrate being polished can be obtained.

In the method for manufacturing the polishing pad, it is preferable forthe polymeric elastomer to be filled into the interior of an ultrafinefiber-entangled body composed of the bundles of the ultrafine fibers insuch a way that void areas in the polishing pad have a volume ratio ofat least 50%.

According to this arrangement, by adjusting the amount of the polymericelastomer filled into the ultrafine fiber-entangled body so as to makethe void volume ratio in the polishing pad of at least 50%, thepolishing pad for polishing bare silicon wafers which has a suitablestiffness and an improved abrasive slurry retention and cushionabilitycan be obtained.

INDUSTRIAL APPLICABILITY

The polishing pad according to the present invention can be used as apolishing pad for polishing various devices, substrates and otherproducts on which planarization or mirror polishing are carried out,examples of which include semiconductor substrates, semiconductordevices, compound semiconductor devices, compound semiconductorsubstrates, compound semiconductor products, LED substrates, LEDproducts, silicon wafers, hard disk substrates, glass substrates, glassproducts, metal substrates, metal products, plastic substrates, plasticproducts, ceramic substrates and ceramic products.

1-10. (canceled) 11: A method for manufacturing a polishing pad, themethod comprising: filling the interior of bundles of ultrafine fiberswhich have an average fineness of from 0.01 to 0.8 dtex with a polymericelastomer having a glass transition temperature of −10° C. or below,storage moduli at 23° C. and 50° C. of from 90 to 900 MPa, and a waterabsorption ratio, when saturated with water at 50° C., of from 0.2 to 5mass %. 12: The method for manufacturing a polishing pad according toclaim 11, wherein the polymeric elastomer is filled into the interior ofan ultrafine fiber-entangled body composed of the bundles of theultrafine fibers such that void areas in the polishing pad have a volumeratio of at least 50%. 13: The method for manufacturing a polishing padaccording to claim 11, further comprising: obtaining a sheet ofentangled webs by stacking and entangling a plurality of filament webscomposed of composite fibers containing a water-soluble thermoplasticresin and a water-insoluble thermoplastic resin; binding fiber bundlesby impregnating the entangled web sheet with an aqueous liquid ofpolymeric elastomer and dry coagulating the elastomer; and formingultrafine fibers by dissolving the water-soluble thermoplastic resin inhot water. 14: A polishing pad, which is obtained by the methodaccording to claim 11.